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    内蒙古阿鲁科尔沁旗陶海营子剖面林西组地球化学特征及其对物源-构造背景的制约

    Geochemical characteristics of Linxi Formation along Taohaiyingzi section in Ar Horqin Banner, Inner Mongolia, and the constraint on the provenances and the tectonic settings

    • 摘要: 大兴安岭中南段上二叠统林西组发育厚层的暗色泥页岩,是区域上重要的上古生界生烃层系之一。阿鲁科尔沁旗陶海营子剖面是林西组的典型剖面之一,本文以该剖面为研究对象,对取自该剖面林西组的10件砂、泥岩样品进行主量元素、微量元素和稀土元素测试分析。剖面样品元素分析和物源判别函数(F1-F2)、Ni-TiO2、La/Th-Hf图解判别结果表明,陶海营子剖面林西组沉积物来源多样,主要来源于上地壳长英质火成物源区和石英岩沉积物源区,还有少量来自中、基性岩火成物源区。剖面样品微量元素PAAS(后太古庙澳大利亚页岩)标准化蛛网图、稀土元素球粒陨石标准化配分模式图、K2O/Na2O-SiO2、Zr/Th、TiO2-(TFe2O3+MgO)图解、物源构造背景判别函数(F1-F2)'的分析判别和剖面样品与不同构造环境砂岩地球化学参数对比结果表明,陶海营子剖面林西组物源构造背景具有被动大陆边缘、活动大陆边缘和大陆岛弧特征,构造背景较复杂。综合分析可知,陶海营子剖面林西组物源主要为被动大陆边缘背景下的火成岩、石英质沉积岩,以及活动大陆边缘和大陆岛弧背景下的火成岩。结合前人相关研究成果,推测兴蒙造山带内伸展作用背景下的晚石炭世-二叠纪岩浆型被动陆缘沉积建造和与俯冲背景有关的古生代弧岩浆岩应该是陶海营子剖面林西组的主要物源。

       

      Abstract: A set of thick-bedded dark muds and shales are developed in Linxi Formation of Upper Permian in south-central part of Da Hinggan Mountains, serving as one of the important Upper Paleozoic hydrocarbon source rock strata in this region. The Taohaiyingzi section in Ar Horqin Banner is one of the most typical sections of Linxi Formation, and the authors took the section as the study area. Test and analysis of major elements, trace elements and rare earth elements were conducted for ten pieces of sand or mud samples of Linxi Formation along the section. The results of element analysis and the diagrams of provenance discrimination function (F1-F2), Ni-TiO2 and La/Th-Hf show that Linxi Formation along the section had several provenances, which mainly included felsic igneous rock provenance and quartzite sedimentary provenance besides a minority of intermediate-basic igneous provenance. Based on the analysis of the spider diagram of trace elements standardized by PAAS, the distribution pattern of rare earth elements standardized by chondrite, the diagrams of K2O/Na2O-SiO2, Zr/Th and TiO2-TFe2O3+MgO and provenance tectonic setting discrimination function (F1-F2)'of the samples of the section, and the sand geochemical parameter contrast between the samples and different tectonic settings, the authors hold that the provenances of Linxi Formation along the section exhibited complex tectonic settings with the characteristics of passive continental margin, active continental margin and continental island arc. The comprehensive analysis shows that the provenances of Linxi Formation of the section consisted of igneous rocks and quartziferous sedimentary rocks under the passive continental margin background, and igneous rocks under the active continental margin and continental island arc background. Combined with the previous related study achievements, it could be concluded that the sedimentary formations of Late Carboniferous to Permian magmatic passive continental margin under extension background and Paleozoic arc magmatic rocks under subduction background in Xing'an-Mongolian Orogenic belt ought to be the primary provenances of Linxi Formation along the section.

       

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