Research On The Numerical Modeling Of Tectonic And Geo-thermal History Of Rifted Continental Margin Basin

The research on the oil and gas exploration of South China Sea deep water area has been put on the agenda. It has important scientific significance and high application value to study the history of tectono-thermal evolution with basin modeling technology for oil and gas exploration of deep water area, and the research on geodynamics of rifted continental margin of South China Sea.This article is mainly about the research of the Cenozoic basin in the middle-northern part of South China Sea's, which belongs to extensional basins. This kind of basin is created from thinned crust due to the extension of curst and lithosphere. The work begins with the interpretation of three seismic profiles of SO49-17,SO49-18,SO49-25 in the research area. The next step is to use balanced section technique with the software of 2D-Move to complete the modeling of tectonic evolution of these three seismic profiles. A program to inverse multi-points stretching factor is designed based on McKenzie(1978) uniform stretching model. Then, the stretching factor distributions of the three seismic profiles are calculated. The heat flows since 23.8Ma of the research area are also calculated using relative formulae.This article mainly studies the tectonic evolution and thermal modeling of deep-water area Cenozoic basin located at the middle-northern part of South China Sea based on the China-Germany cooperative data, and results are as follows:(1) Five sets of strata, which consist of Paleocene-Eocene, Oligocene, lower Miocene, middle Miocene, and upper Miocene-Quaternary, are identified in the continental shelf and continental slope area. (2) The tectonic evolution modeling of three seismic profiles have been completed using balanced section technique with the software of 2D-Move. The results showed that, the extension started from Paleocene-Eocene period and represented as a series of normal faults cutting Mesozoic basement, then rapid sedimentation in downfaulted area, marked the beginning of rifting period. At Oligocene period, extension activity was weakened, regional unconformities began to form, and parts of the tectonic highs were submerged. At early Miocene-middle Miocene period, fault controlled subsidence was weakened, postrift thermal subsidence began, and water depth further increased. Since middle Miocene, extension ceased, sea level rose in general, and the topography framework system of the continental shelf, continental slope and oceanic basin similar to today's one were set up.(3) the inversed stretching factor distributions of three seismic profiles' using uniform stretching model, the best fitting stretching factors are between 1.2 and 2.5.(4)Paleo-heat flows of 23.8Ma,16.5Ma and 10.5Ma of in the research area are calculated base on the inversed stretching factor. The geo-thermal history results demonstrate that the present heat flows are high at the Zhu II depression (include south-western margin of Baiyun depression) located at the north of research area,. In the north part of seismic line 17, the south-western margin of Baiyun depression, the heat flow is 83～90 mW/m~2. In the north part of seismic line 18, the Zhu II depression, the heat flow is 73～80 mW/m~2. In the middle Yitongansha uplift, the heat flow is low. Along seismic line 18 of this area, the heat flow is 70～76 mW/m~2. and along seismic line 25 of this area, heat flow is 68～78 mW/m~2. Heat flow increased in the continental slope area in the south.