Gravity and magnetic anomalies and deep structure in the Sanjiang Basin

The Sangjiang Basin is one of the typical basin among the NE China Basin Groups,which is situated in the northeast of NE china.The analysis of the basin's deep tectonics,including the basement,crustal density,Moho and Curie,will be conducive to the solution of fundamental promblems in geodynamics.This research is based on Bouguer gravity and aeromagnetic anomalies data,combined with other geology data.The gravity and magnetic methods are commonly used in basin structural research which have better horizontal resolution than seismic profiling exploring. Forward and inversion modeling approaches,such as Wavelet Multiscale Decomposition, Logarithmic Power Spectrum Analysis,Horizontal derivative method and Parker method,are utilized in this research.Gravity and magnetic anomalies of the Sanjiang Basin mainly strike NNE and NE,followed by WE,which indicates that the pre-existing WE Paleo-Asian Ocean tectonics domain superposed and modified by the NE Pacific domain.Zoning characteristics of gravity and magnetic fields prove a significant mosaic tectonic background of the study area.Gravity and magnetic fields of Sanjiang Basin are separated with Wavelet Multi-scale Decomposition of order 4.The apparent depths of causative sources were then assessed by Power Spectrum Analysis of each order.Low-order wavelet detail anomalies were used to study the basin's basement structure such as major faults,the basement lithology,uplifts and depressions.High-order ones were used for the inversion of Moho and Curie discontinuities using the Parker method.To extract linear basement faults,the first derivative of the Summation of details of order 2-3wavelet gravity and magnetic is calculated.Finally,5major basement faults are identified in the study area and their occurrence characters are established after the gravity gradient belt characteristics are enhanced.The4 th order gravity magnetic approximation anomalies after Wavelet Multiscale Decomposition may reflect the 3Dshape of the Moho and Curie in the Sanjiang Basin.Based on order 4approximation of gravity anomalies,the Moho depth of the study area is inversed using Parker method.The depth of the study area ranges from 29.5km to 30.5km with high value in the northwest and low value in the southeast,that of the northwestis deep while that of the southeast is shallow.Based on order 4approximation of magnetic anomalies,the Curia depth of the study area is also inversed using Parker method.The Curia depth of the study area ranges from 21 km to 24 km with high value in the north and low value in the south.