Application of the Material Balance Method in Paleoelevation Recovery： A Case Study of the Longmen Mountains Foreland Basin on the Eastern Margin of the Tibetan Plateau

We applied the material balance principle of the denudation volume and sedimentary flux to study the denudation-accumulation system between the Longmen Mountains (Mts.) and the foreland basin. The amount of sediment in each sedimentation stage of the basin was estimated to obtain the denudation volume, erosion thickness and deposit thickness since the Late Triassic Epoch, to enable us to recover the paleoelevation of the provenance and the sedimentary area. The results show the following: (1) Since the Late Triassic Epoch, the elevation of the surface of the Longmen Mts. has uplifted from 0 m to 2751 m, and the crust of the Longmen Mts. has uplifted by 9.8 km. Approximately 72% of the materials introduced have been denuded from the mountains. (2) It is difficult to recover the paleoelevation of each stage of the Longmen Mts. foreland basin quantitatively by the present-day techniques and data. (3) The formation of the Longmen Mts. foreland basin consisted of three stages of thrust belt tectonic load and three stages of thrust belt erosional unload. During tectonic loading stages (Late Triassic Epoch, Late Jurassic–Early Cretaceous, Late Cretaceous–Miocene), the average elevation of Longmen Mts. was lower (approximately 700–1700 m). During erosional unloading stages (Early and Middle Jurassic, Middle Cretaceous and Jiaguan, Late Cenozoic), the average elevation of Longmen Mts. was high at approximately 2000–2800m.