本文選題：開平凹陷 + 構造—地層層序��； 參考：《中國地質(zhì)大學(北京)》2017年碩士論文

【摘要】：開平凹陷位于珠江口盆地珠Ⅱ拗陷的西部,處于南海北部陸緣洋陸過渡帶的位置。構造特征極為復雜,研究程度較低。本文基于最新的鉆井和地震資料,結合前人研究的成果,分析了開平凹陷及鄰區(qū)地質(zhì)結構和構造演化;運用盆地模擬手段,計算了開平凹陷及鄰區(qū)不同構造單元構造沉降量,并在此基礎上,計算了殼幔伸展因子,以此來探討開平凹陷及鄰區(qū)的伸展模式和伸展機制。本次研究主要取得以下成果和認識:1.利用高精度三維地震剖面及鉆井資料,通過不整合面分析表明開平凹陷發(fā)育多個不整合面,其中主洼和北洼發(fā)育六個大的不整合面;西洼和西南洼發(fā)育五個大的不整合面,由此將開平凹陷劃分為七套(或六套)構造層:基底構造層、斷陷一幕構造層、斷陷二幕構造層、斷陷三幕構造層、斷拗期構造層、拗陷期構造層及加速沉降期構造層。不同構造單元不整合面特征存在差異,構造-地層層序特征也存在差異。2.以斷層相關褶皺理論為指導,結合斷層解釋及△T0圖的編制,認為開平凹陷受控于大型伸展拆離斷層,是典型的拆離盆地。根據(jù)拆離斷層幾何學和運動學特征,將斷層分為西南段、中段和東北段。西南段斷層主要為犁式、座椅式和勺狀形態(tài),中段斷層主要為座椅式和勺狀,東北段斷層為犁式。斷層在下文昌組中段沉積期開始活動,在恩平組沉積末期近乎停止活動,三段斷層并在這一時期發(fā)生硬連接作用。西洼和西南洼主要表現(xiàn)為北斷南超的半地塹結構,而主洼和北洼受控于南部和北部斷層的控制,表現(xiàn)為雙向旋轉的特征,具有地塹結構。3.結合人工井點,通過盆地模擬手段,恢復了盆地的沉降史,結果表明開平凹陷及鄰區(qū)49-39Ma構造沉降速率最大,在39-30Ma開始顯著減小,在30-17.5Ma有小幅度的增大,在17.5Ma也有增大現(xiàn)象。結合區(qū)域地質(zhì)背景,認為17.5Ma構造沉降速率小幅度增大與海底擴張停止有關。30Ma左右南海擴張形成的破裂不整合面分割了裂陷期和裂后期地層,之后盆地進入?yún)^(qū)域性熱沉降階段。4.在構造沉降史的基礎上,利用非均勻伸展模型,計算了不同人工井的殼幔伸展因子,由此繪制了剖面的伸展因子分布曲線。結果表明巖石圈地幔伸展因子明顯大于地殼伸展因子,巖石圈地幔伸展因子在1.28-1.45之間變化,地殼伸展因子在1.08-1.3之間變化。地殼伸展因子的分布曲線與新生界沉積基底面大體呈鏡像關系。綜合前人研究及本次研究的結果認為,開平凹陷及鄰區(qū)上地殼屬于簡單剪切伸展模式,具有不對稱結構;下地殼及巖石圈地幔屬于純剪切伸展模式。巖石圈整體表現(xiàn)出非均勻差異伸展變形的特征。
[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.
【學位授予單位】：中國地質(zhì)大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P736.1

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