【作者】 王振涛；

【导师】 王训练；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2014， 博士

【摘要】 鄂尔多斯盆地不仅油气资源丰富，也是我国钾盐找矿远景区。奥陶纪全球蒸发岩形成条件欠佳，但在鄂尔多斯盆地中东部的陕北地区依然沉积了巨厚的岩盐，并且达到了钾镁盐沉积阶段，说明鄂尔多斯盆地奥陶纪具备成盐成钾的古构造、古气候、古地理条件，但一些基础问题仍然悬而未决。本文对鄂尔多斯西、南缘十多条奥陶系剖面进行了详细观察和采样分析，并开展了岩石学、地层学、地球化学、沉积学、地球物理学以及锆石年代学等方面的研究，取得了如下认识：1、通过对鄂尔多斯盆地及周缘高精度、大比例尺航磁异常资料ΔT化极、上延处理，获得了有关磁异常分区信息。航磁化极上延异常图上正、负异常分别与盆地结晶基底的隆起和凹陷大致吻合，表明基底埋深可能是航磁异常的基本控制因素。结合鄂尔多斯盆地基底断裂、基底变质岩与花岗岩锆石SHRIMPU-Pb定年、钻井和碎屑锆石年龄证据，认为鄂尔多斯陆块可能不是一个完整的太古宙陆块；2、在贺兰山地区中奥陶统樱桃沟组首次发现内波、内潮汐沉积和等深流沉积；3、对樱桃沟组碎屑岩进行了地球化学及岩石学分析，认为樱桃沟组物源区主要为主动大陆边缘，也有来自被动大陆边缘的信息。结合中奥陶世鄂尔多斯西缘古水流和碎屑锆石年龄分布特征，认为樱桃沟组的物源主要来自祁连造山带，部分来自阿拉善古陆；4、获得了鄂尔多斯盆地西南缘陕西泾阳西陵沟剖面和甘肃平凉银洞官庄剖面奥陶系平凉组钾质斑脱岩的地球化学特征和锆石U-Pb年龄。地球化学特征表明样品的钾质特征，以及其原始岩浆为高钾亚碱性流纹英安岩和粗面安山岩，多数样品具有典型的岛弧火山岩的特征。通过LA-ICP-MS锆石U-Pb定年，获得了6组谐和年龄。根据钾质斑脱岩区域分布判断其源于南部北秦岭地区或/和西南部北祁连地区的火山喷发。综合分析表明，平凉组多层钾质斑脱岩代表的构造活动期代表了秦岭-祁连洋向北俯冲最强烈的时期，并直接导致了鄂尔多斯盆地南缘奥陶系重大沉积转换。更多还原

【Abstract】 There is growing concern about the Ordos Basin because of its hydrocarbon resources. It should be noted, though, that the Ordos basin is also potash ore prospect areas in China. In the geological background of global poor evaporite deposits, huge rock salt deposited in North Shaanxi Province, located in the central and eastern Ordos Basin, and it achieved the depositional phase of potassium and magnesium salt. These indicate there are paleotectonics, paleoclimate, paleogeographic conditions for potassium salt in the Ordos Basin. Some basic geological problems, however, remain controversial. On the basis of references to the predecessors’ researches, this paper did detailed observation and sampling analysis of field sections in the southern and western margin of the Ordos Basin and conducted the studies of lithology, stratigraphy, geochemistry, sedimentology, geophysics and zircon chronology. Obtained as follows:1. Aeromagnetic anomaly zonation of the Ordos Basin and adjacent areas was obtained by processing high-precision and large-scale aeromagnetic anomalies with an approach of reduction to the pole upward continuation. Basement depth might be the fundamental control factor for aeromagnetic anomalies because the positive and negative anomalies on the reduction to the pole-upward-continuation anomaly maps roughly coincide with the uplifts and depressions of the crystal-line basement in the basin. The results, together with the latest understanding of basement faults, SHRIMP U-Pb zircon dating of metamorphic rock and granite, drilling data, detrital zircon ages, and gravity data interpretation, suggest that the Ordos block is not an entirety of Archean.2. This paper firstly discovered internal-wave, internal-tide deposits and contourite in the Middle Ordovician Yingtaogou Formation in the Helan Mountain area.3. The petrologic and geochemical characteristics of sandstone from Yingtaogou Formation have been researched systematically. The geochemical signatures indicate its double provenance supply feature. After comprehensive consideration of the middle Ordovician palaeocurrents in the western Ordos and detrital zircon age features, we suggest that the provenance of Yingtaogou Formation was mainly the North qilian orogenic belt and the Alashan paleolandmass as a minor one.4. We report the geochemical and zircon U-Pb dating on K-bentonite samples collected from two sections, located in Jingyang County, Shaanxi Province and Pingliang City, Gansu Province. The major elements and the Nb-Zr diagram show the potassium-rich characteristic. Inactive elements in the process of weathering are employed to reconstruct the protolith, and the result demonstates primary magma of the K-bentonites is high-potassium alkaline rhyolitic dacite and trachyandesite. Most of the K-bentonite samples show typical characteristics of arc volcanic rocks, which were probably related to the subduction setting. LA-ICP-MS U-Pb dating on zircons from4K-bentonites samples in Xilinggou profile and2samples from Yindongguanzhuang profile has yielded6sets of concordant ages. Accordingly, the main depositional period of Pingliang Formation, which is still controversial, is redefined to Sandbian-Katian, Late Ordovician. According to their regional distribution, it is thought that these K-bentonites derive from volcanic eruption in the southern North Qinling or/and southwestern North Qilian region. Composite analysis indicates that the important sedimentary turn appearing the south Ordos Basin results from the subduction northward of Qinling-Qilian ocean. Volcanic eruption events represented by these K-bentonites beds have a good coupling relationship with periodic subsidence and filling process of North Qinling back-arc basin (southern margin of Ordos basin).更多还原