## 4 Lithospheric Magnetic Field Model of the Tibetan Plateau
### Geological Structures Analysis of Magnetic Anomalies in the Tibetan Plateau  
The geological structures of the Tibetan Plateau are complex and have a unique and deep tectonic background. The boundary between the northern edge of plateau and the Tarim Basin is the Altun Tagh fault zone. The northeast part of the Tibetan Plateau is the Qaidam Basin. The plateau mainly includes the Songpan-Ganzi block, the Qiangtang-Chengdu block, the Lhasa block, and the Himalaya block from north to south. These blocks are bounded by the LungmuCo-Jinshajiang suture zone, the Bangong-Nujiang suture zone, and the Yarlung-Zangbo suture zone [52; 53] (Figure 8). Figure 6: Contour maps of difference for Z component between R-SCHA model and satellite observation. (**a**) CHAMP satellite observation at 330 \(\pm\) 5 km; (**b**) Swarm satellite observation at 470 \(\pm\) 5 km. Figure 7: RMS distribution with altitude in nT (**a**) and in% (**b**) for X, Y, and Z components. To analyze the relationship between the magnetic anomalies and geological structures of the Tibetan Plateau, a contour map of the lithospheric magnetic field in the Tibetan Plateau at a height of 300 km based on 0.5\({}^{\circ}\)\(\times\) 0.5\({}^{\circ}\) grid resolution is first drawn (Figure 9). The red region in the figure represents the positive anomaly, and the blue region denotes the negative anomaly. The large-background lithospheric magnetic field in the hinterland of the Tibetan Plateau shows the negative anomalies that formed a sharp contrast with positive anomalies observed in the Tarim Basin located in the north, the Sichuan Basin located in the east, and the Indian subcontinent located in the southwest. This demonstrates that an immense difference exists in the basement tectonics of the Plateau hinterland and the surrounding blocks. The midwestern part of the weak magnetic anomaly region is approximately distributed in a strip shape along the east-west direction. This distribution is basically consistent with the orientation of the regional geological structures, and its boundary basically agrees with the boundary of regional tectonic. However, in the east of the plateau, the magnetic anomaly gradually extends along the northeast direction, thereby exhibiting an arc shape. Thus, the magnetic anomaly is inconsistent with the east-south distribution of the geological structures zone. This phenomenon indicates that the anomaly in the east of the plateau may be caused by the magnetic materials in the middle and shallow layers of the earth's crust. Figure 8: Tectonic map of the Tibetan Plateau. AKMS (Ayimaqin-Kunlun Mutztagh suture); ATF (Altryn Tagh fault); BNS (Bangong-Nujiang suture); JRS (Jinsha River suture); YZS (Yarlung-Zangbo suture). Figure 9: Contour map of \(Z\) component of the lithospheric magnetic field at 300 km altitude. The satellite magnetic anomaly map shows that the magnetic anomaly intensity and its distribution in all secondary structures zones in the Tibetan Plateau from the north to the south differ. A regional clump by positive anomaly is distributed in the middle part of the Tarim Basin. The western region adjacent to the Arkin fault zone shows a linear positive anomaly, but the eastern regions adjacent to the Qilian Mountain fault zone exhibit a negative anomaly. However, the positive and negative anomalies are weak. The Songpan-Ganzi block and the Qiangtang-Chengdu block are mainly manifested in a stable negative anomaly that approximates an east-west distribution. The eastern regions near the thrust nappe belt of the Longmen Mountains shows a northeast-southwest negative anomaly. Weak negative anomalies of these blocks imply that the Curie isothermal surface in these blocks is deeper than that in the south of the plateau. Magnetic anomalies in the Lhasa (Gangdise belt) and Himalaya blocks approximately show an east-west orientation along the west section of the Himalaya and across the Himalaya mountains, and this orientation continuously extends to the east region of Lhasa with a distinct negative anomaly.