Isostatic gravity anomalies in the Longmen Mountains and their constraints on the crustal uplift below the mountains on the eastern margin of the Qinghai-Tibet Plateau

The isostatic gravity anomalies on the eastern margin of the Qinghai-Tibet Plateau may be divided into the weak negative isostatic gravity anomaly zone of the Qinghai-Tibet Plateau, positive isostatic gravity anomaly zone of the Longmen Mountains and negative isostatic gravity anomaly zone of the Sichuan basin. The isostatic gravity anomalies did not cause Airy isostatic movements, i.e. no isostatic subsidence occurred in the Longmen Mountains but they were in a continuously uplift state, suggesting that the anti-isostatic tectonic uplift was the main cause responsible for the uplift of the Longmen Mountains. To understand the relationship between the formation of large-scale morphology and the isostatic gravity anomalies of the region, the authors simulated the positive isostatic gravity anomalies of the Longmen Mountains using the similar 3D body gravity anomaly computation method, and the inverse simulation results indicate the top surface of the lower crust below the Longmen Mountains has been uplifted for 11.2-12.6 km, thus causing the positive isostatic gravity anomalies zone of the Longmen Mountains. The authors draw the conclusion that the tectonic uplift and erosion controlled the formation of the morphology of the Longmen Mountains at a similar time and space scale.