鄂尔多斯地块南缘中元古代构造演化特征

发布时间：2018-06-06 00:03

本文选题：鄂尔多斯地块 + 中元古代　；参考：《浙江大学》2015年博士论文

【摘要】：中元古代鄂尔多斯地块构造-沉积演化历来是构造地质学家和石油地质学家们关注的焦点。前人多依据岩石地球化学特征来推测该时期的大地构造背景,本文则主要利用地球物理方法和技术,来解析地块内部中元古代地层结构和构造特征,初步得出如下结论：(1)鄂尔多斯地块内部长城纪沉积层序自下而上可分为二部分：下部与洛南县巡检镇野外露头高山河组下亚段相对应,发育地堑、半地堑,沉积水体局限,沉积环境以陆相三角洲、扇三角洲及水下扇为主；上部与高山河组中-上亚段相对应,沉积水体范围广阔,沉积环境以滨岸、浅海、障壁岛-海岸平原为主。下部层序的几何形态剖面上呈楔形,断裂发育特征表明该时期构造作用强烈；而上部层序厚度变化小、断裂活动减弱。(2)鄂尔多斯地块内部发育蓟县纪碳酸盐岩台地,残余厚度从地块内部向边缘逐渐增大。蓟县纪海-陆边界可能位于余探1井-庆深1井-耀县一线,而岐山县附近出现的事件沉积可能指示台地边缘环境。长城纪的构造地貌可能对蓟县纪碳酸盐岩沉积存在影响,如在旬探1井附近,早期未完全充填的长城纪地堑内水体深度较大,抑制了蓟县纪碳酸盐岩的发育。(3)鄂尔多斯地块南缘中元古界重力低带与重力高带相间排列,重力低带为中元古界厚度较大的地区,主要位于黄陵-旬邑、定边-环县北、绥德南等地区；重力高带为中元古界厚度较小的地区,主要位于吴旗-靖边-榆林、延川-延安-庆阳、合阳-铜川以及盆地西缘。由于蓟县系沿地块边缘分布,厚度小(介于0-1000米),而且钻井岩芯显示地块内大范围缺失新元古界,因此该重力异常主要反映长城系地层厚度的变化。结合地震资料解释,认为重力低带指示长城纪地堑型凹陷,重力高则代表长城纪地垒型凸起。通过对研究区重力异常水平梯度求导,发现区内存在10条区域大断裂：乾县-合阳、麟游-铜川北、灵台北-党家塬-延川、甘泉-清涧、华池-志丹、塬山-饮马沟、扎木音乌素-杨新庄-高家庄、靖边北-榆林北、大水坑-平凉东、白泥井-红旗村。断裂多呈北东走向,断裂控制凹陷和凸起的发育,为同沉积断裂。(4)鄂尔多斯地块南缘中元古界地层结构和构造特征表明,1.8-1.6Ga地块内部及周缘可能受造山后伸展作用形成裂陷,裂陷的发育可能受到早期先存构造的影响,如南部旬邑-黄陵裂陷区与太古代末(2.5Ga)微陆块拼合带重合,在此构造薄弱带基础上发育大规模的地堑,长城系最大厚度超过8000米。持续的裂陷扩张,上述裂陷内充填三角洲相碎屑岩以及滨、浅海相碳酸盐岩和碎屑岩。1.6-1.4Ga,地块南部边缘拉张形成宽坪有限洋盆,地块内发育碳酸盐岩台地,沉积以白云岩为主的一套海相地层。1.4-1.0Ga,为Rodinia超大陆形成时期,北秦岭向鄂尔多斯地块碰撞使得宽坪洋盆逐渐关闭。
[Abstract]:Tectonic-sedimentary evolution of the Ordos block in the Mesoproterozoic era has always been the focus of attention of tectonic geologists and petroleum geologists. In this paper, geophysical methods and techniques are mainly used to analyze the Mesoproterozoic stratigraphic structure and tectonic characteristics of the block. A preliminary conclusion is drawn as follows: (1) the internal Great Wall sedimentary sequence of the Ordos block can be divided into two parts from the bottom to the top: the lower part corresponds to the lower submember of the outcrop Gaoshanhe formation in the wild outcrop of Pouqian Town, Luonan County, and develops graben, semi-graben and limited sedimentary water body. The sedimentary environment is mainly continental delta fan delta and underwater fan and the upper part corresponds to the middle and upper submember of Gaoshanhe formation with a wide range of sedimentary water bodies. The sedimentary environment is mainly shoreline shallow sea barrier island-coast plain. The geometric profile of the lower sequence is wedge-shaped, and the characteristics of fault development indicate that the tectonic action is strong in this period, while the upper sequence thickness changes little and the fault activity weakens. 2) the Jixian carbonate platform is developed in the Ordos block. The residual thickness increases gradually from the interior of the block to the edge. The sea-land boundary of Jixian may be located on the front line of Yuxuan 1 well Qingshen 1 well Yaoxian and the event deposits near Qishan County may indicate the platform margin environment. The tectonic geomorphology of the Great Wall period may have an effect on the carbonate deposits of Jixian period, for example, near well 10 ~ (-1), the depth of water in the early the Great Wall graben is larger than that in the early period. The development of carbonate rocks in Jixian period is restrained.) in the southern margin of Ordos massif, the middle Proterozoic gravity low zone is arranged with the gravity high belt. The gravity low zone is the middle Proterozoic thick area, mainly located in Huangling Xunyi, Dingbian and Huanxian north. The gravity belt is mainly located in Wuqi-Jingbian-Yulin, Yanchuan-Yan'an-Qingyang, Heyang-Tongchuan and the western margin of the basin. Because the Jixian system distributes along the margin of the block with a small thickness (between 0-1000 meters) and the drilling core shows that the Neoproterozoic is missing in a large area within the block, the gravity anomaly mainly reflects the variation of the formation thickness of the Great Wall system. Based on the seismic data interpretation, it is considered that the low gravity zone indicates the Great Wall graben depression, and the gravity high represents the Great Wall crustal uplift. Through the derivation of the horizontal gradient of gravity anomaly in the study area, it is found that there are 10 regional faults in the study area: Qianxian-Heyang, Linyou-Tongchuan north, Lingtai-Dangjiayuan-Yanchuan, Ganquan-Qingjian, huachi-Zhidan, yuan-Yinma gully, Zamuyin-Yang Xinzhuang-Gaojiazhuang, Jingbian North-Yulin North, Da Shui Keng-Pingliang East, Baimud well-Red Flag Village. The faults tend to be northeastward, the fault-controlled depression and uplift are synsedimentary faults. 4) the Middle Proterozoic stratigraphic structure and structural characteristics of the southern margin of Ordos block indicate that the interior and periphery of the 1.8-1.6Ga massif may be formed by post-orogenic extension. The development of the rift may be affected by the early tectonics, such as the overlap zone between the Xunyi and Huangling rifts and the Archean late 2.5 Ga microcontinental assemblage zone. A large scale graben is developed on the basis of this tectonic weak zone. The maximum thickness of the Great Wall system is more than 8000 meters. Continuous rift expansion, the above rifting is filled with delta facies clastic rocks and shoreline, shallow marine carbonate rocks and clastic rocks .1.6-1.4Ga.The southern margin of the block is stretched to form a wide flat limited ocean basin, and carbonate platform is developed in the block. A set of marine strata, .1.4-1.0Ga, which is dominated by dolomite, was formed in the Rodinia supercontinent. The collision of the northern Qinling to Ordos block gradually closed the Kuanping ocean basin.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P548

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