Key geodynamic processes and driving forces of Tethyan evolution

Tethys tectonic system has experienced a long-term evolution history,including multiple Wilson cycles;thus,it is an ideal target for analyzing plate tectonics and geodynamics.Tethyan evolution is typically characterized by a series of continental blocks that separated from the Gondwana in the Southern Hemisphere,drifted northward,and collided and accreted with Laurasia in the Northern Hemisphere.During this process,the successive opening and closing of multistage Tethys oceans(e.g.,Proto-Tethys,Paleo-Tethys,and Neo-Tethys)are considered core parts of the Tethyan evolution.Herein,focusing on the life cycle of an oceanic plate,four key geodynamic processes during the Tethyan evolution,namely,continental margin breakup,subduction initiation(SI),Mid-Ocean Ridge(MOR)subduction,and continental collision,were highlighted and dynamically analyzed to gather the following insights.(1)Breakup of the narrow continental margin terranes from the northern Gondwana is probably controlled by plate subduction,particularly the subduction-induced far-field stretching.The breakup of the Indian continent and the subsequent spreading of the Indian Ocean can be attributed to the interactions between multiple mantle plumes and slab drag-induced far-field stretching.(2)Continental margin terrane collision-induced subduction transference/jump is a key factor in progressive Tethyan evolution,which is driven by the combined forces of collision-induced reverse push,far-field ridge push,and mantle flow traction.Moreover,lithospheric weakening plays an important role in the occurrence of SI.(3)MOR subduction is generally accompanied by slab break-off.In case of the considerably reduced or temporary absence of slab pull,mantle flow traction may contribute to the progression of plate subduction.MOR subduction can dynamically influence the overriding and downgoing plates by producing important and diagnostic geological records.(4)The large gravitational potential energy of the Tibetan Plateau indicates that the long-lasting India-Asia continental collision requires other driving forces beyond the far-field ridge push.Further,the mantle flow traction is a good candidate that may considerably contribute to the continuous collision.The possible future SI in the northern Indian Ocean will release the sustained convergent force and cause the collapse of the Tibetan Plateau.Based on the integration of these four geodynamic processes and their driving forces,a“multienginedriving”model is proposed for the dynamics of Tethyan evolution,indicating that the multiple stages of Tethys oceanic subduction provide the main driving force for the northward drifting of continental margin terranes.However,the subducting slab pull may be considerably reduced or even lost during tectonic transitional processes,such as terrane collision or MOR subduction.In such stages,the far-field ridge push and mantle flow traction will induce the initiation of new subduction zones,driving the continuous northward convergence of the Tethys tectonic system.