The Research Of Potential Data Processing Technique And The Interpretation Of Geological Structure In The South China Sea

The South China Sea is a large marginal sea that develops in the south of China.It is located at the intersection of three plates,with the Pacific plate in the east,the Eurasian plate in the north,and the India-Australian plate in the west and south.The geological structure is complex.The special structural geological background of the South China Sea is also related to the nature of its surrounding continental marginal tectonics: the northern margin of the South China Sea is a passive continental margin,the west is a strike-slip structural edge,and the east is the structural edge of the subduction zone.It is the edge of the extrusion construction.Therefore,it is of great significance to study the boundary of the South China Sea geological body for the division of the South China Sea and the trend and extension of the fault.The study of the open dynamic mechanism of the South China Sea plays an important role in the structural evolution of the South China Sea.Boundary recognition is an important part of the interpretation of the field data.It can indicate the horizontal locations of underground faults,contact zones,and other geological bodies and help us to explain the geological structure.Existing conventional boundary recognition filters are mostly based on gravity gradient data and their horizontal and vertical derivatives.However,these methods have certain limitations: They are sensitive to noise;they can't effectively equalize the amplitude of the depth anomaly;when the measurement anomaly coincides with positive anomalies and negative anomalies,it will produce false boundary results.In the traditional three-dimensional(3D)gravity structure tensor boundary recognizer,the choice of k value has a certain subjective defect: the larger k value can reduce the influence of noise and remove false boundary anomalies,but reduces its ability to equalize.The equilibrium is incomplete;the smaller value of k can well balance the deep shallow anomalies,but it increases the noise interference and can not remove the false boundary anomalies.To solve this problem,this thesis proposes an improved 3D gravity structure tensor method for identifying boundaries,and applies them to synthetic model data and actual geological data of the South China Sea respectively.By comparing the traditional methods,the improved method not only can effectively avoid the defects of the traditional methods,but also obtains a good continuity of the boundary.However,the borders obtained by this method are not sufficiently converged and will interfere with the actual geological interpretation.Further,a new boundary identification method Tilt-Eigen is proposed by obtaining the gradient derivative of the tensor characteristic value of the gravity gradient structure.Through theoretical model experiments and actual South China Sea data processing,and compared with the traditional methods.It shows that this method also overcomes the defects of traditional methods better,and the identified boundary results are more accurate and convergent.The boundary results obtained by Tilt-Eigen are combined with the distribution geological map of the South China Sea Basin,and 20 clear boundary results are obtained and explained accordingly.Based on these boundary results,this thesis concludes that the faults of the western margin of the South China Sea have entered the south side of the Wan'an Basin and have extended toward the WSS,connecting with the faults of the eastern Natuna Basin and finally entering the Kalimantan region in the direction of the ES;Nanao-Haikou After the fault extended to the east side of Hainan Island,it continued to extend toward WWS and entered the Yingge Sea.And it can be seen from this that the fault was faulted by several geological tectonic movements in the later period.In this thesis,the free air gravity anomalies in the South China Sea are subjected to Bouguer correction using the land-land separation method.In the marine area,the traditional Parker-Oldenburg forward model is used to calculate the strata divided into seawater layers,sediment layers,and the basement three layers;on land,it is calculated using traditional ground topography corrections.Finally,the two results are superimposed to obtain the Bouguer gravity anomaly in the South China Sea and explain the anomaly.The gravity anomalies of the South China Sea were divided into eight regions and the corresponding interpretations were made for these regions.In this thesis,the data of magnetic anomalies in the South China Sea are processed by using the method of full-variation dip-polarization.The polar magnetic anomaly of South China Sea was obtained and the anomaly was explained.The polar magnetic anomalies of South China Sea were divided into eight units,which were also divided into eight regions and corresponding interpretations were made for these regions.According to escape Tapponnier et al proposed collision-extrusion-out of the south China sea open mode,again through the south China sea area of gravity,magnetic,seismic reflection profiles and the analysis of seismic velocity data processing,and combining and comparing the information provided by his predecessors,put forward their views about the expansion of the south China sea mode.The specific causes of opening in the south China sea are obtained.: In the collision between the Indochina plate and the Eurasian Plate,because geological orogeny crustal thickness deepens,squeeze out a lot of mantle material,and escape along the red river fault in the direction of ES,In the southern part of Hainan Island,China,the mantle flow turned to the EW to the northwestern sub-basin located along the Xisha Trough fault zone and into the South China Sea.As in the late Eocene and the early Oligocene,the South China Sea and the Liyake Fault were linked to the Xisha Trough,and they broke out along the South China Sea to the mid-ocean ridge.With the development of the left-handed geologic movement in the entire South China Sea,the Zhongnan-Ryori Fault slowly turned from NW to SN and gradually separated from the Xisha Trough,separated by the northwestern sub-basin of the South China Sea.Therefore,the northwestern sub-basin is also slowly opening.However,because most of the Mantle material influx into the central basin,the development of the Northwest sub-basin is incomplete.By analyzing the tectonic origin of the South China Sea,this thesis also put forward its own viewpoints on the tectonic evolution of the South China Sea,and described it as 42Ma~35Ma,32Ma~25Ma,25Ma~21Ma and 21 Ma~17Ma 4 time nodes.