Erosion‐Driven Isostatic Flow and Crustal Diapirism: Analytical and Numerical Models With Implications for the Evolution of the Eastern Himalayan Syntaxis, Southern Tibet

Abstract

The Eastern Himalayan Syntaxis (EHS) is one of the fastest exhuming regions on Earth since ∼10 Ma, and the mechanism of its fast exhumation is under debate. Different from many other studies based on tectonics‐driven models, we performed analytical analysis and numerical simulations to investigate an erosion‐driven system. Our results show that fast and focused surface erosion alone is able to exhume the lower crust on the timescale of ∼10 Myr. This process leads to the formation of a domal structure, an elevated geothermal gradient, rapid cooling of crustal rocks, and decompression melting in the lower crust. In the upper‐mid crust, the uplift of crustal rocks is caused by isostatic flow driven by pressure gradient, whose rate is limited by the driving erosional forcing. In the mid‐lower crust where decompression melting occurs, rocks entrained in a buoyant diapir experience fast uplift rate exceeding the erosional forcing. Our erosion‐driven model demonstrates an intricate coupling between surface erosion and crustal processes. Positive feedback between surface erosion and rock uplift is possible under certain conditions and crustal diapirism plays a key role in the feedback. Our study shows that both isostatic and diapiric flows play important roles in the uplift and exhumation of crustal rocks in the EHS. We highlight that erosion‐driven crustal diapirism can be one of the missing pieces explaining the evolution of the Eastern Himalayan Syntaxis.