Contrasting mechanisms of present-day vertical deformation along the northeastern Tibetan Plateau: Insights from 3-D viscoelastic modeling

Abstract

Summary The northeastern margin of the Tibetan Plateau exhibits pronounced spatial variations in present-day vertical crustal deformation, yet the mechanisms controlling these differences remain debated. In particular, contrasting uplift patterns are observed between the Liupanshan tectonic belt and the Maxianshan Fault, two key tectonic structures along the northeastern expansion front of the plateau. Here we develop two three-dimensional viscoelastic finite element models constrained by geological structures, seismic profiles, and GNSS observations to investigate the controls on vertical deformation. The modeling results show that when the mid–lower crustal viscosity is laterally uniform between the Longxi Basin and the Ordos Block, vertical deformation of ~2 mm/a is concentrated within a ~50 km-wide zone near the Liupanshan tectonic belt, consistent with leveling observations. This deformation pattern mainly reflects crustal shortening and thickening dominated by pure shear. In contrast, the observed ~4 mm/a uplift along the hanging wall of the Maxianshan Fault can only be reproduced when weak mid–lower crust and enhanced crustal flow are introduced beneath the Linxia Basin, indicating that northeastward mid–lower crustal flow is converted into vertical uplift along the fault. These results suggest that the Maxianshan Fault represents the northeastern termination of mid–lower crustal flow within the Qilian Block, whereas deformation in the Liupanshan tectonic belt is primarily accommodated by crustal shortening. Our findings highlight the fundamental role of lateral rheological heterogeneity in controlling vertical deformation and provide new insights into the mechanisms of present-day lateral growth of the northeastern Tibetan Plateau.