贺兰山地区晚三叠世延长期物源属性及其构造意义

发布时间：2018-01-30 19:43

本文关键词： 贺兰山晚三叠世物源分析古构造背景物源时空演化　出处：《西北大学》2015年硕士论文　论文类型：学位论文

【摘要】：贺兰山地区晚三叠世的物源来源以及时空演化规律,是恢复鄂尔多斯盆地西部北段原盆边界,分析盆地内沉积地层时空展布特征和沉积相演变规律的重要环节,是客观评价改造盆地油气资源分布特征以及科学预测盆地有利勘探区块的重要前提和基础。贺兰山地区处于多构造单元的结合部位,经历了复杂的沉积构造演化历史,研究贺兰山晚三叠世物源属性必须要考虑这些因素的影响。通过对贺兰山周边构造单元演化过程的系统分析,论文重点考虑了古亚洲洋闭合过程与勉略洋闭合过程对贺兰山地区晚三叠世沉积演化的影响,并认为当时贺兰山地区可能为被动拉张背景下的裂谷环境。此外,还重点考虑了晚侏罗世大地构造运动以及新生代银川地堑、河套盆地形成过程中对研究区晚三叠世地层的后期改造特征。结合贺兰山地区的区域构造背景和后期改造程度,运用地层变形恢复的方法,对研究区主要断层的断距以及小块体的相对位置进行了恢复和复原,合理推断了贺兰山地区晚三叠世的沉积边界范围。论文主要运用古水流分析、砾石成分分析、地球化学、薄片鉴定、阴极发光以及重矿物组合分析等方法对研究区物源进行了综合研究。认为贺兰山晚三叠世的物源具有多源、混源以及上下层段时空演化差异性明显的特点。晚三叠世的物源主要有西北部、西部和东部物源,并在汝箕沟-香棒子沟一带发生混源。西北部物源主要为阿拉善地块之上的前寒武纪变质岩、古生代岩浆岩及沉积地层,西部南段地区可能与西部北段的物源岩性有较明显不同；东部地区物源可能为鄂尔多斯地块之上的古生代沉积地层。通过对延长组五个层段物源特征的对比研究,认为不同时期物源方向具有一定的差异。延长组一段、二段、三段主要物源来自西北部和西南部,这时贺兰山盆地和鄂尔多斯盆地之间是连通,而且连通范围较广,到了延长组四段、五段时,在荒草滩及其以东地区开始明显出现东部物源,此时贺兰山盆地和鄂尔多斯盆地之间仍然是连通的,由于汝箕沟沟口东部地区已经隆起,连通的范围开始缩小,这几个方向的物源在汝箕沟-香棒子沟一带发生混源,之后沿着大水沟一带流入鄂尔多斯盆地。结合区域构造环境和邻区的构造特征,指出贺兰山地区晚三叠世延长期的物源性质在研究区的不同部位存在明显差异,并尝试性地建立了物源的时空演化模式。
[Abstract]:The provenance and spatiotemporal evolution of the late Triassic in Helanshan area is an important link in restoring the basin boundary in the northern part of the western Ordos basin and analyzing the temporal and spatial distribution characteristics of sedimentary strata and the evolution law of sedimentary facies in the basin. It is an important premise and foundation for objectively evaluating the distribution characteristics of oil and gas resources in the reformed basin and scientifically predicting favorable exploration blocks in the basin. The Helanshan area is located in the combination of multiple structural units. After a complicated history of sedimentary tectonic evolution, the influence of these factors must be considered in studying the provenance of late Triassic in Helan Mountain. The evolution process of tectonic units around Helan Mountain is systematically analyzed. The paper focuses on the influence of paleo-Asian ocean closure process and Mianluo ocean closure process on the sedimentary evolution of the late Triassic in Helanshan area, and considers that the Helanshan area at that time may be a rift environment in the passive extensional background. The late Jurassic geotectonic movement and the Cenozoic Yinchuan graben are also considered. In the process of formation of Hetao Basin, the late Triassic strata were reformed in the study area. Combined with the regional tectonic background and the degree of late transformation in Helanshan area, the method of formation deformation restoration was used. The fault spacing of the main faults and the relative position of the small blocks in the study area are restored and restored, and the sedimentary boundary range of the late Triassic in Helanshan area is reasonably inferred. The paleocurrent analysis is mainly used in this paper. Gravel composition analysis, geochemistry, sheet identification, cathodoluminescence and heavy mineral assemblage analysis were used to study the provenance of the studied area. It is considered that the late Triassic provenance of Helan Mountain has multiple sources. The main provenances of late Triassic are northwest, west and east. The main provenances in the northwest are Precambrian metamorphic rocks, Paleozoic magmatic rocks and sedimentary strata. The source lithology of the southern part of the west may be obviously different from that of the northern part of the west. The material source in the eastern area may be Paleozoic sedimentary strata above the Ordos block. Through the comparative study of the characteristics of the five layers of Yanchang formation, it is considered that there are some differences in the direction of provenance in different periods and one section in Yanchang formation. The main provenance of the third member is from the northwest and southwest. At this time, it is connected between the Helanshan basin and the Ordos basin, and has a wide range of connectivity, when the fourth and fifth member of the Yanchang formation. The eastern provenance began to appear in the wasteland and its east area, and the connection between Helanshan basin and Ordos basin was still connected at this time, because the eastern area of Rujigou gully mouth had been uplifted, the connected area began to shrink. These material sources are mixed in Rujigou and Xiangliangzigou, and then flow into Ordos basin along Dashuigou, combining with the regional tectonic environment and the structural characteristics of the adjacent area. It is pointed out that the provenance properties of the extension period of the late Triassic in Helanshan area are obviously different in different parts of the study area, and the spatio-temporal evolution model of the provenance has been established.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.13

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