鄂尔多斯盆南部延长组凝灰岩地球化学特征

Geochemical Characteristics of Tuff in Yanchang Formation of Southern Ordos Basin

鄂尔多斯盆地南部地区延长组凝灰岩为特殊时代背景下通过一系列沉积产生的沉积岩,深入分析并探究凝灰岩代表的古构造环境,对识别盆地在构造演化过程发育的类型、分析鄂尔多斯南部区域与秦岭造山带之间的盆地山脉耦合关系有着重要意义。通过扫描电镜、能谱分析以及主微量元素等多种分析测试手段,对鄂尔多斯盆地南部地区延长组凝灰岩地球化学特征进行了详细分析,研究表明:该区域凝灰岩主要为长石和黏土类矿物组成,表现为火成岩性质,主要来源于古大陆架边缘以及大洋孤岛,具有明显的区域分布和多期形成的特征。并将现有的凝灰岩按照其成因类型划分为3类:火山灰蚀变相对较弱、以黏土矿为主、重稀土元素相对平缓的凝灰岩;火山灰蚀变强烈、以黏土矿为主、重稀土元素相对亏损的斑脱岩;Ba含量相对较高、发育硅质条带或硅质岩、重稀土元素相对富集的凝灰岩。

The tuff of Yanchang formation in the south of Ordos basin is the sedimentary rock produced by a series of deposition under the special age background. The deep analysis and exploration of the paleotectonic environment represented by tuff are of great significance to identify the type of basin developed in the process of structural evolution and analyze the basin mountain coupling relationship between the south of Ordos basin and Qinling orogenic belt. The geochemical characteristics of tuff in Yanchang formation in the south of Ordos basin were analyzed in detail by means of SEM, EDS and major and trace elements. The results showed that the tuff in this area is mainly composed of feldspar and clay minerals, which are of igneous nature and mainly come from the edge of the ancient continental shelf and the isolated island of the ocean, have the characteristics of domain distribution and polyphase formation. The existing tuff can be divided into three types according to their genetic types: the tuff with relatively weak pozzolanic alteration, dominated by clay ore and relatively gentle HREE;the porphyry with strong pozzolanic alteration, dominated by clay ore and relatively deficient HREE;the tuff with relatively high Ba content, developed siliceous strip or siliceous rock and relatively enriched HREE.