Discrete Element Modelling of Southeast Asia’s 3D Lithospheric Deformation during the Indian Collision

The Indian collision has deformed the eastern Asian continent in a multifaceted way, uplifting Tibet and surrounding mountains, activating ≥ 1000 km-long strike-slip faults, and opening Tertiary rifts and oceanic basins up to ≈ 3000 km away from the Himalayas. Modelling such broad-scale tectonics has been challenging. While continent-scale, lithospheric deformation appears to have been primarily taken-up by long, narrow, inter-connected shear-zones with large offsets, the contribution of processes such as channel-flow, collapse, delamination, etc… has remained contentious. Here, based on increasing 4G (Geological, Geophysical, Geochronological, Geodetic) evidence including kinematic and timing constraints on the main mechanisms at play, we use Discrete Element (DE) Modelling to simulate and further understand the evolution of 3D strain across east Asia since the onset of collision, ≈ 55 Ma ago. The planar, 50 million km2, 125 km-thick models are scaled for gravity. The approach permits mega-fault generation and evolution without pre-arranged initial settings. The results provide insight into fault birth, propagation, and motion, as well as mountain building and plateau growth. They corroborate that continental crustal thickening across Tibet alternated with the extrusion of large blocks that rifted apart in the far field. Remarkably, without changes in boundary conditions or indentation rate, the DE model also vindicates slip reversal along initial strike-slip shear zones.