武威盆地石炭系泥页岩元素地球化学特征及意义

发布时间：2018-02-10 07:05

本文关键词： 武威盆地石炭纪元素地球化学构造背景物源风化作用　出处：《现代地质》2017年03期 　论文类型：期刊论文

【摘要】：对武威盆地及其周缘区石炭系的臭牛沟组和羊虎沟组沉积泥页岩样品进行了主量元素、微量元素以及稀土元素的综合分析,并讨论其结果对物源、风化剥蚀程度及构造背景的指示意义。研究发现武威盆地石炭系泥页岩元素特征如下:(1)主量元素中富含SiO_2、Al_2O_3,亏损MgO、Fe_2O_3;(2)微量元素上地壳标准化曲线呈规律性的变化,U、Th、Cr等元素富集,Ba、Nb、Zr等亏损;(3)稀土元素(REE)分布模式与上地壳基本一致,整体表现为右倾型,轻稀土(LREE)富集,重稀土(HREE)均一稳定,Eu负异常;上述特征均反映了源岩主要来自上地壳。风化指数(CIA)值为68.81~90.17,平均值为83.9,反映了研究区遭受了中等的风化作用;臭牛沟剖面CIA平均值为84.81,红水堡剖面CIA平均值为83.51,表明研究区西部较东部所遭受的风化作用相对较强。主量元素比值、微量及稀土元素图解等分析反映了研究区源岩为长英质岩石,以中酸性花岗岩、碱性玄武岩为主。根据SiO_2-K_2O/Na_2O、La-Th-Sc和Th-Co-Zr/10判别图解以及Ce异常值分析,认为石炭系源区的构造背景倾向于被动大陆边缘。通过研究区东西对比分析,发现盆地西部臭牛沟剖面石炭系为陇西古陆与阿拉善古陆混合物源,而东部红水堡剖面物源仅来源于陇西古陆。
[Abstract]:The main elements, trace elements and rare earth elements in the sedimentary shale samples of the Carboniferous and Yanghugou formations of the Carboniferous in the Wuwei Basin and its surrounding area were analyzed, and the results were discussed. It is found that the elements of Carboniferous shale in Wuwei Basin are characterized as follows: 1) the main elements are rich in SiO2Al2O3, depleted MgO2Fe2O3 and 2) the crustal standardization curves of trace elements show a regular change. The REE) distribution pattern of REE) is basically consistent with that in the upper crust. All the above characteristics reflect that the source rocks mainly come from the upper crust. The weathering index (CIAs) is 68.81g / 90.17 and the average value is 83.9, which reflects the moderate weathering in the study area. The average value of CIA was 84.81 in the ShuNiugou section and 83.51 in the Hongshuibao section, indicating that the weathering in the western part of the study area was relatively stronger than that in the eastern part of the study area. The analysis of trace and REE diagrams shows that the source rocks in the study area are felsic rocks, mainly intermediate-acid granite and alkaline basalt. According to SiO2-K _ 2O / Na _ 2O / Na _ 2O-T _ 2O / Na _ 2O-Th-Sc and Th-Co-Zr/10 discriminant diagrams and ce anomaly value analysis, It is considered that the tectonic background of the source area of the Carboniferous tends to be passive continental margin. By comparing and analyzing the east and west parts of the study area, it is found that the Carboniferous in the western part of the basin is a mixture of Longxi ancient land and Alashan ancient land. In the eastern part of Hongshuibao section, the provenance was only originated from the ancient land of Longxi.
【作者单位】：中国地质大学(北京)能源学院;中国地质大学(北京)页岩气勘查与评价国土资源部重点实验室;
【基金】：基金项目:中国地质调查局“河西走廊重点盆地烃源岩调查”(12120115002901-04)
【分类号】：P595;P618.13

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