Numerical simulations on the present-day convergence pattern along the Himalayan orogenic belt

Himalayan orogenic belt is one of the most geodynamically active and tectonically complex regions in the world, driven by the continuous compression and collision between the Indian and Eurasian continents since ~55 Ma. Investigations on its deformation mode and dynamic mechanisms has become a hot spot in the geoscience research. Although some studies preliminarily explained the local deformation feature around the belt, detailed dynamic simulations based on tectonic backgrounds and rheological properties are still limited and the convergence pattern along the Himalayan arc is still controversial. Therefore, we adopt the 3D finite element numerical simulations to build the Radial, Oblique and Viscoelastic Convergence Models constrained by the GNSS velocities, and further to reveal the deformation mechanism and dynamic patterns along the Himalayas. Compared to the Radial Convergence Model, Oblique Convergence Model provides a better fit to the GNSS observations, indicating that the convergence between the Indian and Eurasian plates involves not only a radial motion (18 mm·a−1) but also the arc-parallel motions (2 mm·a−1 and 14 mm·a−1 in the central and eastern segments, respectively). Accordingly, the tectonic dynamics of the widespread extensional rifts in the southern Tibetan Plateau are likely attributed to oblique convergence along the boundary faults of the Indian and Eurasian plates, which differs from the hypotheses of gravitational collapse or the lithospheric-mantle convection. On the other hand, the Viscoelastic Convergence Model incorporating the regional rheological properties shows the best fit to the far-field GNSS data, compared to the elastic Convergence Model. It suggests that the tectonic stress may trigger stable far-field viscoelastic deformation, and the dynamic processes can be better and more reasonable simulated by the viscoelastic model. In addition, the fully coupled depth on the boundary fault estimated by the viscoelastic model is 16 km, slightly shallower than that derived from the elastic model. Our works provide a basis for understanding of the potential deformation patterns and plate collision mechanisms along the Himalayas based on the numerical simulations.