Gravity and Magnetic Field Characteristics in the Covered Area of Eastern Segment of the Qilian Orogenic Belt and the Delineation of the Northern and Central Qilian Tectonic Boundaries

The eastern segment of the Qilian orogenic belt is situated at the northeastern edge of the Qinghai-Tibetan Plateau, intersecting with the Alxa Massif and Ordos Massif. This region also serves as a transitional zone between the Qinling orogenic belt and the Qilian orogenic belt. The tectonic framework in this region is highly complex, and the current understanding of the boundaries between the north Qilian and central Qilian tectonic units remains relatively limited. In this study, we applied the normalized vertical derivative of the total horizontal derivative (NVDR-THDR), minimum curvature field separation, and wavelet multi-scale decomposition to process and analyze Bouguer gravity anomalies and the magnetic anomalies reduced to the pole. By integrating regional geological characteristics, we inferred four primary faults and fifty-four secondary faults. The primary faults delineate the boundaries of tectonic units. Specifically, the boundary between the Qilian and North Qilian tectonic units is traced by a linear segment connecting Ping'an-Ledu-Dingxi-Zhangjiachuan, corresponding to the northern edge fault of the Qilian Mountains. Furthermore, there exists a prominent first-class tectonic unit known as the north Qilian accretionary wedge between central Qilian and north Qilian units. The eastern coverage area of the Qilian orogenic belt can be divided into three tectonic units: the northern Qilian island arc belt, the Northern Qilian accretionary wedge, and the central Qilian rogenic belt.