被动大陆边缘洋陆过渡带构造数值模拟及成因机制：开平凹陷例析

发布时间：2018-05-28 19:31

本文选题：开平凹陷 + 构造—地层层序　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：开平凹陷位于珠江口盆地珠Ⅱ拗陷的西部,处于南海北部陆缘洋陆过渡带的位置。构造特征极为复杂,研究程度较低。本文基于最新的钻井和地震资料,结合前人研究的成果,分析了开平凹陷及邻区地质结构和构造演化;运用盆地模拟手段,计算了开平凹陷及邻区不同构造单元构造沉降量,并在此基础上,计算了壳幔伸展因子,以此来探讨开平凹陷及邻区的伸展模式和伸展机制。本次研究主要取得以下成果和认识:1.利用高精度三维地震剖面及钻井资料,通过不整合面分析表明开平凹陷发育多个不整合面,其中主洼和北洼发育六个大的不整合面;西洼和西南洼发育五个大的不整合面,由此将开平凹陷划分为七套(或六套)构造层:基底构造层、断陷一幕构造层、断陷二幕构造层、断陷三幕构造层、断拗期构造层、拗陷期构造层及加速沉降期构造层。不同构造单元不整合面特征存在差异,构造-地层层序特征也存在差异。2.以断层相关褶皱理论为指导,结合断层解释及△T0图的编制,认为开平凹陷受控于大型伸展拆离断层,是典型的拆离盆地。根据拆离断层几何学和运动学特征,将断层分为西南段、中段和东北段。西南段断层主要为犁式、座椅式和勺状形态,中段断层主要为座椅式和勺状,东北段断层为犁式。断层在下文昌组中段沉积期开始活动,在恩平组沉积末期近乎停止活动,三段断层并在这一时期发生硬连接作用。西洼和西南洼主要表现为北断南超的半地堑结构,而主洼和北洼受控于南部和北部断层的控制,表现为双向旋转的特征,具有地堑结构。3.结合人工井点,通过盆地模拟手段,恢复了盆地的沉降史,结果表明开平凹陷及邻区49-39Ma构造沉降速率最大,在39-30Ma开始显著减小,在30-17.5Ma有小幅度的增大,在17.5Ma也有增大现象。结合区域地质背景,认为17.5Ma构造沉降速率小幅度增大与海底扩张停止有关。30Ma左右南海扩张形成的破裂不整合面分割了裂陷期和裂后期地层,之后盆地进入区域性热沉降阶段。4.在构造沉降史的基础上,利用非均匀伸展模型,计算了不同人工井的壳幔伸展因子,由此绘制了剖面的伸展因子分布曲线。结果表明岩石圈地幔伸展因子明显大于地壳伸展因子,岩石圈地幔伸展因子在1.28-1.45之间变化,地壳伸展因子在1.08-1.3之间变化。地壳伸展因子的分布曲线与新生界沉积基底面大体呈镜像关系。综合前人研究及本次研究的结果认为,开平凹陷及邻区上地壳属于简单剪切伸展模式,具有不对称结构;下地壳及岩石圈地幔属于纯剪切伸展模式。岩石圈整体表现出非均匀差异伸展变形的特征。
[Abstract]:Kaiping sag is located in the western part of Zhujiangkou basin and located in the transitional zone of oceanic land in the northern margin of the South China Sea. The structural characteristics are very complex and the research degree is low. Based on the latest drilling and seismic data, combined with the results of previous studies, the geological structure and tectonic evolution of Kaiping sag and its adjacent areas are analyzed, and the tectonic subsidence of different structural units in Kaiping sag and adjacent area is calculated by using basin simulation. On this basis, the extensional model and the extensional mechanism of Kaiping depression and its adjacent areas are discussed by calculating the extensional factors of crust and mantle. This study mainly achieved the following results and understanding: 1. Using high precision 3D seismic profile and drilling data, the unconformity surface analysis shows that there are many unconformities in Kaiping sag, in which six large unconformities are developed in main and northern depression, and five unconformities are developed in Xiwa and southwest depression. Therefore, Kaiping sag can be divided into seven sets (or six sets) of structural layers: basement layer, fault depression one scene structure layer, fault depression second act tectonic layer, fault depression three act tectonic layer, fault-sag period structural layer, depression period structural layer and accelerated subsidence period structural layer. The unconformity surface features of different tectonic units are different, and the characteristics of tectonic-stratigraphic sequence are also different. Under the guidance of fault-related fold theory combined with fault interpretation and compilation of T0 diagram it is considered that Kaiping depression is controlled by large extensional detachment fault and is a typical detachment basin. According to the geometric and kinematic characteristics of the detachment fault, the fault is divided into the southwest segment, the middle section and the northeast section. The faults in the southwest part are plow type, seat type and ladle type, in the middle segment they are seat type and spoon type, and in the northeast part they are plough type. The fault started to be active in the middle part of the lower Wenchang formation, and nearly stopped at the end of the deposit period of the Enping formation, and the three sections of the fault formed a hard connection in this period. Xiwa and southwest depression are mainly semi-graben structure with north fault and south superstructure, while main depression and north depression are controlled by the control of southern and northern faults, showing the characteristics of bidirectional rotation, with graben structure .3. The subsidence history of the basin is restored by means of basin simulation combined with artificial well points. The results show that the subsidence rate of 49-39Ma structure in Kaiping sag and adjacent area is the largest, which decreases significantly in 39-30Ma, increases slightly in 30-17.5Ma and increases in 17.5Ma. Combined with the regional geological background, it is considered that the small increase of 17.5Ma tectonic subsidence rate is related to the depression of the South China Sea about .30Ma, and the fracture unconformities formed in the South China Sea, dividing the rift period and the late faulted strata, and then the basin enters into the regional thermal subsidence stage .4. Based on the history of tectonic subsidence, the crust-mantle extensional factors of different artificial wells are calculated by using the inhomogeneous extension model, and the distribution curves of the extensional factors in the profile are plotted. The results show that the lithospheric mantle extensional factor is obviously larger than the crustal extensional factor. The lithospheric mantle extensional factor varies from 1.28-1.45, and the crustal extensional factor varies from 1.08-1.3. The distribution curve of crustal extensional factors is mirrored with the sedimentary basement of the Cenozoic. It is concluded that the upper crust of Kaiping depression and its adjacent area belong to a simple shear extension model with asymmetric structure and that the lower crust and lithospheric mantle belong to a pure shear extension model. The lithosphere as a whole shows the characteristics of heterogeneous differential extensional deformation.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P736.1

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