【作者】 逯东霞；

【导师】 姜常义；

【作者基本信息】 长安大学 ， 矿物学、岩石学、矿床学， 2007， 硕士

【摘要】 贺兰山地区地处分隔中国东、西部两大构造带的北段。其明显的地貌特征、特殊的构造样式、“多旋回”式的构造活动备受地学界的瞩目。该地区是一个长期活动的区域,奥陶纪是其沉积构造演化的重要阶段。本文在充分整理现有资料及前人研究成果的基础上,通过系统的岩相学、沉积学、元素地球化学、沉积环境和沉积相的研究,探讨了贺兰山地区在早、中奥陶世期间沉积盆地类型及其演化历史,取得了以下几点初步认识:1、贺兰山在早奥陶世末期—中奥陶世为半深水—深水相的沉积组合,其岩性主要为碎屑岩、泥岩、碳酸盐岩,岩石组成较为复杂,岩相变化急剧。2、米钵山组由碎屑流沉积、泥石流沉积和浊流沉积等沉积相组成,重力流沉积发育,属大陆斜坡坡脚地带的海底扇沉积。沉积微相包括角砾岩微相、具逆粒序层理的岩屑杂砂岩微相、同沉积改造作用较强的砾屑灰岩微相,这些微相组合具有大陆边缘的微相组合特征。3、元素地球化学性质研究表明其沉积界面以还原性为主,局部还原环境较强;沉积速率快,具大陆斜坡重力流快速堆积特征。4、沉积地球化学证据表明,米钵山组的物源具有活动陆缘及岛弧性质,综合考虑贺兰山所处的区域构造背景,物源可能来自于南部的北祁连地区。5、早奥陶世晚期,贺兰山地区的沉积构造格局发生明显变化。中南部地区进入快速拉张阶段,发育碳酸盐重力流沉积;由于区域构造活动加剧,沉降幅度加大,陆源碎屑重力流活动频繁;之后,构造活动趋于平稳,水体变深,为深水盆地充填。至中奥陶世末期,海水逐渐变浅,为滨海—浅海相沉积。6、在早奥陶世末期,贺兰山位于北祁连弧后盆地靠陆一侧,受弧后扩张作用以及阿拉善地块与中朝板块之间相对运动的影响,重新开始了拉张、沉降,形成了被动型裂陷盆地一贺兰冷裂谷。中奥陶世末期,随着北祁连古洋盆的逐渐关闭,该冷裂谷遭受改造而消亡。更多还原

【Abstract】 Helan mountain is situated in the northern part of South-North trending structural zone which lies between different tectonic realm of east and west china. It is focused on obvious geomorphic character, special tectonic pattern, "multicycle" tectonic activity. This area is a long term active region, its important constituted section of sedimentary tectonic evolution is Ordovician. According to the systematic research of petroface, microelements, rare earth elements and sedimentary environment, based on full reorganization existence information and in predecessor research results, we discuss its sedimentary type of Ordovician, we obtain several preliminary understanding as follows:1. The sedimentary combination is half deep water-deep aqueous phase from early Ordovician late stage to middle Ordovician at Helan mountain, its main lithology is clastic rock, argillite, carbonatite, The rock composition is complex and petrographical facies change sharply.2. Miboshan formation is composed by these sedimentary facies such as debris-flow sedimentary mud flow turbidite sedimentary and so on, the gravity flows is developed, it belongs to Continental slope region submarine fan deposition. The sedimentary microfacies includes breccia microfacies counter grain of foreword lamination rock microfacies strong affection calcirudite with the deposition transformation microfacies, these microfacies compositions has the character of continent edge microfacies composition.3. The element geochemistry research natures shows that the sedimentary interface was mainly reduction, partial reductional environment was strongly; the sedimentary rate was fast, and it had the character of continent pitch gravity flow fast accumulation.4. The synthesis considered the regional structure background of Miboshan formation in Helan Mountain, its activity epicontinental and the resource of the arc nature possibly comed from the south northern Qilian area.5. The sedimentary structure of Helan Mountain area changed obviously in laest Early Ordovician.The south area fast extendly and grown gravity-current carbonate; Because the areal structure activity intensifies, the subsidence scope enlarges and terrigenous clastics gravity current flowed frequently; Afterwards, the structure activity tends to steadily, the water level changed deeply, belong to deep basin. To latest Middle Ordovician, the sea water gradually changed shallowly, were littoral-neritic deposit.6. In latest Early Ordovician, We think that Helan Mountain area that lied in the northern Qilian back-arc basin where near to the continent possibly affected by the back-arc expansion and the relative motive of the Alashan massif and sino-korean massif, and it restarted to expansion subside, and formed passive rifited basin—Helan cold rift. In latest Middle Ordovician, affected by Qilian ocean closed, this cold rift vanished because of the reformation.更多还原