东海与南海北部盆地构造演化及其对煤系烃源岩的控制作用

发布时间：2018-08-11 15:54

【摘要】：盆地的形成及构造演化控制着其沉积充填及层序地层格架,由此奠定了烃源岩的形成与发育。宏观盆地群在区域构造背景控制下具有一定的构造和沉积响应,不同构造演化阶段烃源岩生成与分布具有一定的规律性。本文在系统总结前人有关东海与南海盆地形成机制研究的基础上,选取盆地内典型含煤凹陷(东海西湖凹陷、南海北部琼北坳陷带与白云凹陷),利用同沉积断裂活动特征分析与平衡剖面技术,探讨不同动力学机制控制下的盆地构造与演化特征及其差异性,基于构造坡折带对煤系沉积可容空间控制作用的研究,揭示了东海与南海北部盆地煤系烃源岩形成模式及其对盆地构造演化的响应。取得了以下主要研究成果和认识。1、探讨了东海与南海北部盆地的形成及演化历史。东海与南海北部盆地同为新生代伸展断陷盆地,均具有下断上坳的构造体系。前者为印欧板块碰撞的远程作用区,受太平洋后撤俯冲的影响,经历了残余弧后断陷、邻区盆地扩张产生的挤压坳陷和区域热沉降的演化过程。后者则为印欧碰撞的主应力释放区,初始断陷发生于挤出地幔底流拖曳与古南海向南俯冲消亡的联合拉张背景,新南海扩张在盆地裂陷的基础上叠加一期韧性裂陷,海盆扩张脊的跃迁促进了盆地的坳陷,海盆扩张结束导致了最终的热沉降阶段。2、深入分析了煤系烃源岩的形成及构造控制作用。煤系烃源岩均形成于盆地的断陷末期,对应于区域上构造转折时期,同沉积构造坡折带对煤系空间展布起到了决定性的控制作用,西湖凹陷平湖组形成于太平洋俯冲方向由NNW向NWW的转向期,盆缘SE侧断裂对太平洋俯冲作用反应敏感,受同沉积断裂的控制,煤系沉积仅限于凹陷NW侧缓坡坡折带区域;琼东南北部坳陷带崖城组形成于南海海底扩张初期,同沉积断裂活动稍弱,同沉积陡坡与缓坡坡折带均具煤系沉积,但煤系沉积在凹陷内部不连续;受区域位置与基底先存构造的影响,海底扩张在白云凹陷恩平组沉积期间叠加一种韧性沉降,凹陷整体呈现同沉积缓坡坡折带,煤系分布较为广泛。3、基于聚煤坳陷沉降机制的研究,提出了伸展和断坳两大类型聚煤模式。在研究凹陷聚煤期间的沉降机制研究的基础上,将聚煤模式分为伸展聚煤型和断坳聚煤型两大类。伸展聚煤型以基底的幕式断陷和掀斜伸展为特征,聚煤沉积向缓坡带迁移致使陡坡带缺失煤系沉积,由此可进一步分为单一缓坡聚煤和双侧坡带聚煤,西湖凹陷属于单一缓坡聚煤模型,琼北坳陷带则为双侧坡带聚煤;白云凹陷断陷末期在韧性沉降变形机制为主导构造作用控制下,形成断坳聚煤盆地。
[Abstract]:The formation and tectonic evolution of the basin controlled its sedimentary filling and sequence stratigraphic framework, which laid a foundation for the formation and development of the source rocks. The macro-basin group has a certain structural and sedimentary response under the control of regional tectonic background, and the source rock generation and distribution in different tectonic evolution stages have certain regularity. On the basis of systematically summarizing the previous studies on the formation mechanism of the East China Sea and South China Sea basins, this paper selects the typical coal-bearing sag in the basin (Xihu Sag in the East China Sea). In the Qiongbei depression and Baiyun sag in the north of the South China Sea, the characteristics and differences of basin structure and evolution under the control of different dynamic mechanisms are discussed by using the characteristics of synsedimentary fault activity and balanced profile technique. Based on the study of the controlling effect of structural slope break zone on the accommodation space of coal measures, the formation model of coal measure source rock in the basins of the East China Sea and the northern part of the South China Sea and its response to the tectonic evolution of the basin are revealed. The formation and evolution history of the basins in the East China Sea and the northern part of the South China Sea are discussed. The basins in the East China Sea and the northern part of the South China Sea are both Cenozoic extensional faulted basins with the structural system of lower fault and upper depression. The former is the remote action area of the Indo-European plate collision, which is affected by the Pacific retreat and subduction, and has undergone the evolution process of the residual back-arc fault depression, the compression depression and the regional thermal subsidence caused by the basin expansion in the adjacent area. The latter is the principal stress release area of the Indo-European collision. The initial fault depression occurred in the combined extensional setting of the extrusion mantle bottom drag and the subduction of the ancient South China Sea to the south. The new South China Sea extension superimposed a first stage ductile rift on the basis of the basin rift. The transition of the spreading ridge of the basin promotes the depression of the basin, and the end of the basin extension leads to the final thermal subsidence stage .2. the formation and tectonic control of the source rocks of coal measures are deeply analyzed. The source rocks of coal measures are formed at the end of the fault depression of the basin, corresponding to the tectonic transition period in the region. The synsedimentary structural slope break zone plays a decisive role in controlling the spatial distribution of the coal measures. The Pinghu formation in Xihu sag was formed during the shift from NNW to NWW in the subduction direction of the Pacific Ocean. The SE fault in the margin of the basin was sensitive to the subduction of the Pacific Ocean, controlled by the synsedimentary faults, and the coal-measure deposits were confined to the region of the gentle slope break zone of the NW side of the sag. Yacheng formation in the northern depression zone of southeastern Hainan Province was formed in the early stage of sea floor expansion in the South China Sea. The synsedimentary fault activity was slightly weak, and both the synsedimentary steep slope and the gentle slope break belt were deposited in coal measures, but the coal measures deposits were not continuous in the sag. Under the influence of regional location and basement preexisting structure, undersea expansion superimposed a kind of ductile subsidence during the deposition of the Enping formation in Baiyun depression, and the whole sag presented the same sedimentary gentle slope break zone. Coal measures are widely distributed. Based on the study of subsidence mechanism of coal accumulation depression, two types of coal accumulation models, extensional and fault depression, are proposed. Based on the study of the subsidence mechanism during coal accumulation in the sag, the coal accumulation model is divided into two types: extensional coal accumulation type and fault depression coal accumulation type. The extensional coal accumulation type is characterized by the episodic fault depression and tilting extension of the basement. The migration of coal accumulation deposition to the gentle slope zone leads to the absence of coal measure deposition in the steep slope zone, which can be further divided into single gentle slope coal accumulation and double side slope zone coal accumulation. Xihu sag belongs to a single gentle slope coal accumulation model, while the Qiongbei depression zone is a double slope zone, and the late Baiyun depression is dominated by ductile subsidence and deformation mechanism to form a fault depression coal accumulation basin.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.13

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