Abstract:

It is still controversial what drives crustal movement. Although there are many competing theories, the magnitude of the driving force described in these theories is too small to drive crustal movement. In addition, many in-situ stress measurements showed that the horizontal principal compressive stress is the largest of the three in-situ stress components and considered as the crustal “anomaly” pressure, however, there is no unified mechanistic explanation for this observation. Therefore, it is necessary to find out what the source of the driving force is and why such horizontal stress dominants. Inspired by anticlinal structures and stone arch bridge that are supported by lateral force, and through stress analysis of the Earth model, we concluded that the crust, as a spherical shell, can experience lateral extrusion from its own weight, which acts as circumferential-direction stress. Consistent with the in-situ measured stress characteristics, this circumferential-direction stress is derived from and greater than gravity. We estimated that the stress is about 900 MPa at 20 km depth, enough for driving plate movement (needs at least 500 MPa). Because, as asthenosphere can flow, stress will be released as long as there is a weak zone in the lithosphere above it, resulting in relative motion between plates. The whole oceanic crust behaves like an arch bridge: under circumferential-direction stress, it can insert into the deep part of the continental crust at the subduction zone, the weak area of the lithosphere, so the subduction zone bears part or even all of the weight of seafloor. Finally, we proposed that there is no structural force or collision force independent of gravity that can work independently, the circumferential-direction stress is the only driving force strong enough for crustal movement.

Key words: circumferential-direction stress, plate movement, geodynamic force, mantle convection, gravity and tectonic movement