Potential Field Characteristics And Tectonic Division In Dasanjiang Region

"Dasanjiang Basin" is located in northeastern Heilongjiang Province in China,which consists of a series of Mesozoic-Cenozoic rift basin groups, It’s an importantdistribution area of metal and non-metallic mineral resources such as coal, oil, gas etc.in China and also one of our key research areas of petroleum exploration. At presentthe degree of geophysical exploration in research area is lower, and the systematicresearch using large-scale potential field data for unit structure in this area is stillblank. Therefore, it has some practical significance to discuss the data processingmethods of potential field that are suitable for the fracture plane distribution and todivided tectonic units in this area. In this thesis, we collected and processed thegravity and air-magnetic anomaly data with1:200000scale in Dasanjiang region, andgot the potential field anomalies lines of main fracture. Combined with results ofprevious studies and relevant geological information, we divided the major faults andtectonic units of the research area.In the thesis, the main body content and solutions of the problems as follows:1. Aiming at the problem that the regular boundary identification methods haveweak or haven’t the capacity of discernment for small-scale, shallow-depth geologicalboundary, we came up with the enhanced horizontal gradient on the basis of thenormal derivative analysis of potential field anomalies. In model tests, in contrast withtotal horizontal gradient, Theta map, Tilt angle, the total horizontal gradient of tiltangle, normalized standard deviations and small subdomain filtering, it’s reasonableand has advantages. On this basis, the gravity anomalies in Dasanjiang Basin wereanalyzed by using this method. Combined with the regular boundary identificationmethods and optic properties inversion results, we identify plane positions of14faultswith better continuity. Combined with regional tectonic evolution history, the cuttingrelations among the faults formed in different stages were analyzed.2. In order to suppress the amplification effect on high frequency components in the process of downward continuation, improve the stability and resolution ofnormalized full gradient of gravity, combined normalized full gradient of gravity wereproposed through designing combination filter of regularization factor and downwardcontinuation factor. In petroleum model tests, the regularization parameters α, themaximum value of GHand the relationship between its vertical position and harmonicnumber N were analyzed in the process of calculation. Through the comparativeanalysis, the method presented in this thesis has strong recognition ability to thedifferent scale reservoir. By using this method, the profile data of bouguer gravityanomalies in Qianjin depression in Dasanjiang basin was calculated, and favorablegas-oil potential was predicted.3. Base on the characteristics of gravity and magnetic field and residual field,optic properties inversion results, distribution of faults and regional geology inDasanjiang region, tectonic units were divided. First-class tectonic units are boundedby Mudanjiang fault and Dahezhen fault, and form the west to east the research area isdivided into Songnen block, Jiamusi-Xingkai block and Wandashan terrane in turn.Second-class tectonic units are bounded by Jiamusi-Yitong fault, Dunhua-Mishanfault and Dahezhen fault. The Songnen block is divided into Xiaoxing’anling blockand Zhangguangcailing block, the Jiamusi-Xingkai block is divided into Jiamusiblock and Xingkai block, and the block in the east of Dahezhen fault is WandashanBlock.4. The gravity residual filed and apparent density inversion results shows that thedistribution characteristics and strength of negative residual field anomaly trap andnegative apparent density trap, correspond with Dunhua-Mishan fault depression,Tangyuan-Fangzheng graben, Qianjin depression and Suibin depression, are similar.The resistivity section through Tangyuan graben, Dunhua-Mishan fault depressionand Qianjin depression shows that their structure of electricity are low resistance,high resistance and low resistance from top to bottom, which called "sandwich". Thisgeophysical field structure styles provide geophysical evidences for the geologicalunderstanding, which the eastern Heilongjiang basin group was a unified basin withforeland basin properties in early Early Cretaceous, namely "Dasanjiang Basin".5. Base on the anomaly characteristics performed by the gravity and magnetic field and its data processing results and the resistivity distribution characteristics ofgeoelectric section,"Dasanjiang Basin" is the area delineated by Jiamusi-Yitong faultand Jiamusi-Xingkai Block boundary fault, is fault basin group consist of Tangyuanbasin, Sanjiang basin, Shuangyashan basin, Boli basin,Dunmi basin, etc.