Contribution of the Rheologically Weak Lower Crust to Contemporary Crustal Motions in the Southeastern Tibetan Plateau, China

The southeastern Tibetan Plateau (SETP) plays a pivotal role in accommodating intra‐continental deformation driven by the ongoing India‐Eurasia convergence. However, its contemporary surface vertical motions and the underlying geodynamic processes remain highly debated. Previous studies have proposed that spatial variations in lithospheric rheology govern intracontinental deformation and orogenesis. Here, based on a 2D viscoelastic model and geodetic observations, we infer the laterally varying lower crustal viscosity across the SETP, where is characterized by lithospheric heterogeneity, as indicated by seismic velocity and electrical resistivity anomalies. The optimal model reveals the lower crustal viscosities of 10 20−21 and 10 18−19 Pa s underneath the Songpan‐Ganzi Block and the Xiaojiang region, respectively, and exceeding 10 21 Pa s underneath the central Yunnan Block and South China. Such a heterogeneous lower crustal rheological structure can explain the geodetically observed regionally variable surface vertical motions. Particularly, it reconciles the apparent inconsistency related to surface uplift in the absence of upper crustal horizontal shortening across the SETP. Our findings highlight the role of lower crustal viscoelastic deformation in modulating surface vertical uplift in the absence of significant upper crustal shortening, and demonstrate that the rheologically weak lower crust complements existing models, including tectonic extrusion and gravitational collapse, to accommodate contemporary crustal motions in the SETP. Furthermore, we argue that lithospheric rheological heterogeneities play an essential role in controlling surface deformation within the context of continental extrusion.