After studying the eastern and western tectonic syntaxis in the Qinghai—Xizang (Tibetan) Plateau, and the tectonic syntaxis in the Izu region of Japan and Taiwan, it is found that the upper crustal mantle of these four typical tectonic junctions has a common structure: the crustal and lithospheric mantle contain upwelling low- velocity anomalies, while the middle and lower asthenosphere have concentrated convex high- velocity anomalies. The following explanations are proposed for the dynamics of the formation of this crust—mantle structural mode: the intersection of the two groups of ocean- to- continent or continent- to- continent subduction zones squeezes and collides with each other, resulting in the fragmentation of end- part of the relatively weak ocean block. The fragmented high- density oceanic lithospheric blocks sink into the asthenosphere, and at the same time cause the thermal fluid in the upper layer of the asthenosphere to upwell, and finally form a tectonic knot, which also produces the crust—mantle structure characteristics of low and high anomalies of seismic wave velocity.