南海北部陆缘白云凹陷盆地构型及其形成演化机制

发布时间：2018-08-11 10:04

【摘要】：本文基于新采集、全盆覆盖的三维地震资料以及跨区域、深层的长电缆地震剖面,从盆地边界断层的识别和盆地属性的厘定入手,系统开展白云凹陷盆地结构构造样式以及发育演化过程的定性和定量研究。研究发现了南海北部陆缘深水区大型拆离断层,确定了白云凹陷为大型拆离盆地的成因属性,探讨了南海北部陆缘岩石圈非瞬时伸展破裂过程,取得了以下主要研究进展和认识成果。1.在白云凹陷深层发现了控制盆地南部边界大型拆离断层。在剖面上拆离断层具有整体向北倾斜、上陡下缓、向下汇聚到莫霍面的宏观趋势,在平面上则为向SE凸出的弧形展布。在凹陷的西部,中部和东部,拆离断层系统构造样式分别表现为断阶式、单断式和复杂的坡坪式。拆离断层的发现为厘定白云凹陷的拆离盆地的地质属性提供了关键证据,具有重要的理论意义和实际应用价值。2.针对拆离盆地开展了盆地充填序列中不同级别层序晃面的识别、标定、追踪和闭合,建立了盆地新生代以来的构造地层格架。特别确定了对应拆离断层强烈活动开始和结束的构造层序界面SD和PD,区分出有别于陆架浅水盆地的拆离层序,并由此将盆地同裂陷阶段的演化划分为高角度正断层控制的断陷幕、大型拆离断层控制的拆离幕和断拗转换幕,明确了不同构造幕的盆地原型以及拆离幕的独特性。3.运用古落差法和回剥技术开展了白云凹陷重要断层活动初期的几何学形态、断裂活动性和盆地沉降史的定量研究。研究表明主拆离断层活跃于中始新世晚期,切割并破坏了早期断陷盆地结构,盆地沉降中心具有由早期的多中心分散分布到拆离幕和拗陷幕单中心聚集的时空分布和迁移规律。以主干剖面为基础,重建了白云凹陷的构造地层发育演化过程。4.剖析了裂谷盆地破裂不整合界面的本质含义,明确了其所代表的是陆缘岩石圈裂解的响应界面。以白云凹陷为例,阐明了盆地断拗转换界面和破裂不整合界面的关系,提出南海陆缘不同构造单元盆地断拗转换面具有非等时性,破裂不整合界面不能代表盆地的“裂后不整合界面”的认识。5.开展了白云凹陷基底岩石圈结构和伸展程度的研究,进一步证实了该凹陷发育在强烈薄化的地壳之上,局部可能为地幔出露区。伸展、薄化程度定量计算表明,白云凹陷主体区域表现出深度相关的伸展,但是在极度薄化区域,沿拆离断层的水平构造活动基本可以调节整个地壳的伸展。提出白云凹陷是南海北部岩石圈经历伸展、薄化、剥露和裂解的“非瞬时”伸展破裂过程中,发育在陆缘细颈化带内的、以简单剪切变形机制形成的陆缘拆离盆地,深水油气勘探前景广阔。
[Abstract]:Based on the three dimensional seismic data of new acquisition, full basin coverage and long cable seismic profiles across regions and deep layers, this paper starts with the identification of basin boundary faults and the determination of basin attributes. The qualitative and quantitative study on structural style and evolution process of Baiyun depression basin is carried out systematically. A large scale detachment fault in the deep water area of the northern continental margin of the South China Sea has been found. The genetic properties of Baiyun Sag as a large detachment basin have been determined, and the process of noninstantaneous extensional rupture of the lithosphere in the northern margin of the South China Sea has been discussed. Achieved the following major research progress and understanding of the results. 1. A large detachment fault at the southern boundary of the control basin was found in the deep layer of Baiyun Sag. In the profile, the detachment fault has a macroscopic tendency of inclining north, rising steeply and slowly down, converging down to the Moho surface, while the plane is an arc of SE protruding. In the west, middle and east of the depression, the structural styles of the detachment fault system are faulted terrace type, single fault type and complex slope flat type, respectively. The discovery of the detachment fault provides the key evidence for determining the geological properties of the separated basin in Baiyun sag, and has important theoretical significance and practical application value. The identification, calibration, tracing and closure of different order sequences in the basin filling sequence are carried out for the purpose of separating the basin, and the tectonic stratigraphic framework of the basin since the Cenozoic is established. In particular, the tectonic sequence interface SD and PDs, which correspond to the beginning and end of the strong activity of the detachment fault, are determined, and the detachment sequence, which is different from the shallow water basin of the continental shelf, is distinguished. The evolution of the same rifting stage in the basin is divided into fault curtain controlled by high angle normal fault, detachment curtain controlled by large detachment fault and fault receding curtain. The basin archetype of different tectonic episodes and the uniqueness of detachment curtain are determined. A quantitative study on the geometry, fault activity and basin subsidence history of important faults in Baiyun sag was carried out by using paleo-drop method and backstripping technique. The results show that the main detachment faults were active in the late Middle Eocene, which cut and destroyed the structure of the early faulted basin, and the subsidence center of the basin has the temporal and spatial distribution and migration law from the early multi-center dispersion distribution to the single center aggregation of the detachment curtain and the depression curtain. Based on the main section, the tectonic stratigraphic evolution process of Baiyun sag was reconstructed. The essential meaning of fracture unconformity interface in rift basin is analyzed, and the response interface of continental lithosphere cracking is defined. Taking Baiyun sag as an example, the relationship between fault-sag transition interface and fracture unconformity interface is clarified, and the non-isochronicity of fault-sag transition mask in different tectonic unit basins of South China Sea continental margin is proposed. The fracture unconformity interface does not represent the understanding of "post-fracture unconformity interface" in the basin. The lithosphere structure and extensional degree of the basement of Baiyun sag are studied. It is further proved that the depression is developed on the strongly thinned crust and may be a mantle outcrop area. The quantitative calculation of extensional and thinning degree shows that the main area of Baiyun sag shows depth-dependent extension, but in the extreme thinning area, the horizontal tectonic activity along the detachment fault can basically regulate the extension of the whole crust. It is suggested that Baiyun Sag is a "non-instantaneous" extensional fracture process of the lithosphere in the northern South China Sea, which is formed by simple shear deformation mechanism and developed in the continental margin fine neck zone during the process of "non-instantaneous" extension and rupture. Deep water oil and gas exploration has broad prospects.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P618.13;P736.1

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