| The Songliao Basin,located between the North China Plate and Siberia Plate,has always been a hot area for academic research due to the over-episodic tectonic movement in this area.On the basement properties,the distribution of fractures and the depth of Moho,No consensus has been reached,and proof of geophysical evidence is needed.Gravity and magnetic exploration is a geophysical method with a wide range of work and large coverage area.It has strong applicability in basin structures and can well detect deep structures.Therefore,this paper adopts a combination of gravity and magnetic methods to study the geophysical characteristics of Songliao Basin.The bouguer gravity anomaly data and aeromagnetic ?T anomaly data scale used in this study are all 1:500000.And Bidimensional empirical mode decomposition,logarithmic power spectrum analysis,gravity and magnetic correlation analysis,the Park-Oldenburg method are used to analyze the problems which contain the distribution of faults in Songliao Basin,the characteristics of basement lithology,the distribution of the sag and uplift and the buried depth of Moho.The actual gravity and magnetic data exist aliasing effect,the data has nonlinear,non-stationary characteristics.Bidimensional Empirical Mode Decomposition is superior in dealing with nonlinear and non-steady-state signals and can achieve multi-scale decomposition of gravity and magnetic data.First of all,the feasibility of Bidimensional Empirical Mode Decomposition in the aspect of regional-residual denoise and separation is verified by the cuboid model and the sphere combination model.After that,by decomposing Bouguer gravity data and aeromagnetic ?T anomaly data in Songliao Basin and using logarithm power spectrum analysis method,the approximate buried depth of field source reflected by the modal components at all levels is estimated.And the results can qualitatively or semi-quantitatively explain the Geological significance of the field source.By comparing with the results of conventional methods,the effectiveness and superiority of this method are further illustrated.First of all,this method has the adaptability of decomposition,which can decompose the data in multi-scale and has higher resolution.Secondly,each component of the decomposition has more detailed information For example,in the result of gravity decomposition,the BIMF component can reflect the internal fracture morphology,spreading direction and size of the basin.This is unmatched by conventional methods.A comprehensive analysis of the gravity BIMF components,original gravity anomalies,aeromagnetic anomalies and distributions of basement fractures describes the abnormal morphology of fractures and their corresponding effects with geological fractures.The study founds that there are 4 groups of deep faults,mainly including basement faults and crustal faults.The directions are NE-NNE,NW-NNW,north-south and east-west.However,the size and amount of the east-west and north-south faults and the clarity of identification are far less than the NE-NW faults,so it can be inferred that the overlying periods of tectonic superimposition occurred in the Songliao Basin.The NE-trending tectonic movement transformed the east-west and north-south faults to form the current structural fracture system.Gravity and magnetic correspondence analysis method can combine the gravity and magnetic data.Through gravity and magnetic correspondence analysis,we can know the lithologic distribution information of the base.Combined with the results of bidimensional empirical mode decomposition and basal outline of the tectonic framework of the basin,the basement lithology distribution of the basin is outlined.Based on the lithology analysis of the basement,it is found that the Indosinian and Yanshanian granites are distributed in the eastern and northern parts of the basin,while the Caledonian and Hercynian granites are distributed in the central and western parts of the basin.The strike of the granite is parallel to the faults inside the basin.Most of the granites are mainly in the NE direction,and the controllability of the basement fault zone to the magmatic activity is inferred.Eventually,the lithology of the basement is unevenly distributed.The Park-Oldenburg method was used to inverse the basement and Moho of the Songliao Basin in combination with the drilling data of Daqing.The buried depth of the basement of Songliao Basin is between 8 and 12 km,with the characteristics of uneven arrangement.The buried depth of less than 9 km is defined as a uplift,more than 10 km of the location is defined as a depression.According to the regional geological conditions,9 main basin depressions and 6 main uplifts were finally confirmed in the basin.According to the results of bidimensional empirical mode decomposition,the BIMF5,BIMF6 and Res components of Bouguer gravity anomaly can reflect the anomaly produced by Moho.The Parker-Oldenburg method was used to invert the Moho in the Songliao Basin and its surroundings.Based on the previous understanding of the study area,the Moho area was divided into three regions based on its depth,shape and fluctuation.The western part is located to the west of the daxing'anling fault zone with a depth varying between 34 and 40 km.The anomaly is north-north east.Songliao Basin is located in the central region,the average depth of Moho is 32 km,ranging from 30.4 ~ 34.2km.The area of xiaoxing'anling corresponds to the sinking area of the Moho,reaching a depth of 34 km.The depth of the Moho is large and the gradient is steep.The southern part of the Songliao Basin is generally located at the Siping.The depth of the Moho is relatively shallow,roughly 31 km,corresponding to the uplift belt of the Moho.The Moho depth is from 30 km to 32 km in Southeast uplift.The eastern part of the Songliao Basin corresponds to the Zhangguangcailing and Sanjiang Basin areas in the gravity division.The area of Zhangguangcailing is the crustal sinking area with a depth of over 34 km.The shallowest area of the Moho is in the Sanjiang Basin,roughly 31 km. |
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