Abstract：The broadband seismic survey and aeromagnetic anomaly study show that the lithosphere below the southern part (i.e. Qinghai-Tibet plate) of the West Kunlun tectonic belt was subducted beneath the Tarim basin and that the ophiolite belt of the West Kunlun is the relics of the Paleo-Tethys ocean that closed during the Caledonian orogen． Due to the strong resistance from the rigid old Tarim terrane during the subduction of the Qinghai-Tibet plate, the north-subducting lithosphere broke up and delaminated. Meanwhile, the rebound of the Qinghai-Tibet lithosphere and buoyancy of the asthenosphere caused extensional downfaulting of the upper crust, which allowed the molten magma at depth to upwell, thus resulting in eruption of alkaline magma along the faults. Furthermore, this also formed an antithetic thrust tectonic framework on both sides of the tectonic belt. The West Kunlun Central fault is actually the “fourth suture” of the Qinghai-Tibet Plateau, whereas the North Kunlun tectonic belt just formed by thrusting of the material at the shallow crustal level in the West tectonic belt over the Tarim foreland during delamination of the lithosphere of the Qinghai-Tibet plate.