武威盆地石炭系泥页岩元素地球化学特征及意义

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SiO2、Al2O3，亏损MgO、Fe2O3；(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SiO2-K2O/Na2O、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。

Element Geochemical Characteristics of Carboniferous Shale in Wuwei Basin and Its Significance

By comprehensively analyzing the major element, microelement and rare earth element of carboniferous shale samples which from Chouniugou Formation and Yanghugou Formation in Wuwei Basin and its surrounded area, and discussing the significance of the result for provenance, weathering denudation degree and tectonic setting. The research founded that the element characteristics of Carboniferous shale in Wuwei Basin is as follaws: (1) The major element is rich in SiO2 and Al2O3, and loss of MgO and Fe2O3. (2) The upper crust standardization of microelements is regularly change. U, Th and Cr are rich, and Ba, Nb and Zr are loss. (3) The distribution pattern of rare earth element (REE) is about the same as upper crust, which is right deviation in overall, rich in LREE, stabilize in HREE and negative anomaly Eu. The three findings show that the source rock is mainly from upper crust. Weathering index (CIA) value of 6881-9017, with a mean of 839, reflects the research area suffered moderate weathering; the average CIA value of Chouniugou section and Hongshuipu section is 841 and 8351 in order which shows that the weathering degree in the western study area is relatively stronger than that in the eastern. The index of weathering(CIA) is relatively high, which indicates the study area is suffered from medium weathering. Analysis of the diagram of major element ratio, microelement and rare earth element indicates the source rock of the study area is feldspathic quartz, mainly intermediate to acidic granite and alkali basalt. On the basis of discrimination diagrams of SiO2-K2O/Na2O, La-Th-Sc, Th-Co-Zr/10 and abnormal value of Ce, the tectonic setting is considered to be a passive continental margin. By contrastive analysis of the east and the west of the study area, we found that Chouniugou section in the west of the Basin has a mixed source from Longxi ancient land and Alashan ancient land, whereas Hongshuipu section in the east of the Basin has a single source from Longxi ancient land.