Lithospheric Rheology and Crustal Deformation Across the Northeastern Tibet and Their Implications for Plateau Growth.

Understanding lithospheric rheology is crucial in investigating tectonic evolution of intra‐continental tectonic boundary. Here, we use geodetic observations to infer lithospheric rheology across the northeastern Tibet based on a 2D viscoelastic model. Our findings reveal a lower‐crust viscosity of <1022 Pa·s underneath its margins, lower than those estimated underneath its vicinities. By comparing deformation patterns and lithospheric rheology here with those observed in the eastern Tibet, we propose that lateral variations in lower‐crust viscosity control deformation patterns and topographic gradients along the Tibet margins. The presence of low viscosity lower‐crust can lead to the development of contrasting topographic gradients and shape the plateau's geomorphology and deformation characteristics during outward growth of the Tibet. We here emphasize the subtle variations in the lower‐crust rheology between deforming blocks and the corresponding mountain ranges, which play an important role in orogeny along the intracontinental convergence boundary. Plain Language Summary: The Tibetan Plateau undergoes remarkable outward growth driven by the ongoing convergence between the Indian and Eurasian plates. Significant questions remain as to the mechanisms responsible for generating distinct topography and deformation patterns along the Tibet margins, particularly when it encounters surrounding rigid continental blocks. The presence of these blocks poses a unique challenge in understanding processes that shape the plateau's geomorphology and deformation characteristics. Here we use geodetic observations to infer the lithospheric rheology across the northeastern Tibet based on a 2D viscoelastic model. We show that the lower‐crust viscosity underneath the margin of northeastern Tibet is notably lower compared to those of underneath its surrounding areas. By comparing these findings with the distinct topography, deformation patterns, and lithospheric rheology observed across the eastern margin of Tibet, we propose that lateral variations in lower‐crust viscosity between active tectonic blocks control the formation of mountain range‐fronts. The weak lower‐crust underneath the mountain ranges exerts a significant influence on uplift dynamics, determining the location of the maximum surface uplift and topographic gradient. Key Points: We infer lithospheric rheology across the northeastern Tibet using geodetic observations based on a 2D viscoelastic modelThe interpretation of surface deformation patterns requires a low viscosity wedge underneath the margin of northeastern TibetThe maximum surface uplift is predicted where the lower‐crust viscosity is the lowest along the intra‐continental convergence boundary [ABSTRACT FROM AUTHOR]