Separation of the field source and characterization of the deep and shallow tectonics of the northwestern margin of the Sichuan-Yunnan rhombic massif

Abstract

Abstract The Sichuan-Yunnan block, characterized by complex geological formations and persistent high-intensity seismicity, remains a focal domain for contemporary geodynamic research. To investigate the fracture depth of the northern Sichuan-Yunnan block and the southeastern part of the Qiangtang block, CRUST1.0 was employed to fit the trend items in the study area and to refine the gravity field model with measured data as control points. A two dimensional discrete wavelet transform analysis method is applied to separate the field sources from the obtained high-precision grid data. Additionally, radial logarithmic power spectrum analysis is utilized to estimate the average equivalent source depth of the abnormal geological bodies corresponding to each order wavelet, thereby extracting both transverse and longitudinal tectonic characteristics of the crust in the region. The results reveal that the Bouguer gravity anomaly within the study area exhibits a general pattern of low values in the northern region and high values in the southern areas. Major faults, including the Bianba-Luolong fault, Nujiang fault, Lancangjiang fault, Batang fault, Jinshajiang fault, Yushu-Ganzi fault and Ganzi-Litang fault are all deep and large faults, with respective depths of 38.9 km, 52.9 km, 52.9 km, 52.9 km, 38.9 km, 52.9 km, 52.9 km. This study provides physical insights into the crustal structure distribution of the northern Sichuan-Yunnan rhombohedral block.