Characteristics Of Gravity And Magnetic Anomalies And The Significance Of Geological Structure In North China Craton And Its Adjacent Areas

North China Craton is one of the three ancient cratons in China.It has a special geological tectonic setting and evolution process and occupies an important position in understanding the geological tectonic evolution of China.The study of the distribution characteristics of gravity and magnetic anomalies in the North China Craton and its adjacent areas reveals its tectonic significance and is of great significance for understanding the geological structure of the North China Craton.In this paper,the NGDC720 geomagnetic model and the EGM2008 and WGM2012 gravity models are used to study the distribution characteristics of spatial distribution and gravity anomalies of crustal magnetic anomalies in North China Craton and adjacent areas at different altitudes.In order to study the magnetic basement undulation and crustal thickness,the magnetic anomaly power spectrum method was used to invert the Curie isothermal surface and the Moho surface was inferred by the Parker-Oldenburg method of Bouguer gravity anomaly.Based on the seismic and geothermal flow data,the structural significance of gravity and magnetic anomaly characteristics,interior and Moho distribution is discussed.The results show that:(1)The spatial distribution of gravity and magnetic anomalies in the North China Craton and its adjacent areas is basically consistent with the geological structure of the area.Strip magnetic anomalies at all mountains in the study area are consistent with the tectonic trend.From the north to the south,the Ordos block in the western North China Craton is an east-west positive magnetic anomaly,a northeast-oriented negative magnetic anomaly,and a north-north-east positive magnetic anomaly that forms an anomalous distribution characteristic from southwest to northeast,and the Qinghai-Tibet Plateau The turn of the gravity anomaly in the northeastern margin and the Qinling orogenic belt verified that the tectonic evolution of the study area was affected by the collision of the Indian-Eurasia plate collision to the northeast.The positive and negative Bouguer gravity anomaly transition lines in the study area suggest that the line may be balanced by the two movements of the Indian-Eurasia plate collision and the western Pacific plate subduction,that is,part of the north-south gravity gradient zone of the Chinese mainland.(2)The depth of the eastern part of the North China Craton is shallower than that of the central and western regions,which is consistent with the conclusion that the eastern part of other disciplines is thinning.The depth of the isotherm in the southwestern margin of Ordos in the west is shallow,corresponding to its strong geothermal value.In addition,there are a large number of historical earthquakes on the west side of the Longmenshan orogenic belt,which can be presumed to be due to the collision of the Indian-Eurasian plate.The uplift of the Qinghai-Tibet Plateau caused the deep matter to flow to the northeast,and was blocked by the rigid Ordos block,which led to the strong deformation of the lithosphere in the southwestern margin of the Ordos block,and caused the local high-temperature melting mantle material migration and upper part of the Ordos block and the surrounding area.The depth of the isothermal surface of the Curie is shallow.The flowing material encounters the force of the Bayan Hara and Longmenshan orogenic belts,making the already unstable structure more prone to earthquakes,and speculates that the strong activity causes degaussing in the area,and the magnetic anomaly The figure shows a strong negative magnetic anomaly.This also indirectly proves that the impact of Erdos's northeastward compression on the Qinghai-Tibet Plateau uplift caused by the collision of the Indian-Eurasian plate is stronger than that of the Pacific plate,(3)The depth distribution of the Moho surface in the study area shows a shallow layout in the west and the east,and the northeast-facing gradient belt at the northeastern margin of the Qinghai-Tibet Plateau indicates the escape direction of the Qinghai-Tibet Plateau.The depth of the Moho surface of the plain fold belt in the eastern part of the North China Craton is not much different from the depth of the Moho surface at sea.This may be related to the thinning of the eastern part of the North China Craton.