プレート運動と大陸移動の原動力－再考

Abstract

The establishment of the theory of plate tectonics at the end of the s provoked quantitative discussions regarding the forces acting on lithospheric plates. Subsequent studies during the early-to mids considered plate motions as rigid rotations on a spherical surface. A theoretical analysis based only on tectonic information from the Earth s surface revealed that a candidate for the primal driving force of plate motion was slab pull , which may be balanced almost completely by slab resistance . However, because plate interiors of the real Earth have finite effective viscosity and are part of the cold thermal boundary layers involved in mantle convection, they should move with an element of internal deformation rather than perfectly rigid motion. A recent numerical simulation of -D spherical mantle convection revealed that the breakup of Pangea, subsequent continental drift, and the present-day continental distribution, could be acheived by planetary-scale mantle flow. Large-scale lateral mantle flow is inferred to have originated from a high-temperature anomaly region beneath Pangea due to a supercontinental thermal insulation effect, rather than by mantle upwelling flow from a superplume , and subduction of cold boundary layers is inferred to have spontaneously developed in the North Tethys Ocean during the early stages of the breakup of Pangea. The present results, combined with other numerical simulation results and seismological evidence from a recent sub-seafloor structure survey, indicate that the (continental) mantle drag force , enhanced by mantle flow beneath the continental/oceanic plates, could be the primal driving force of plate motion and continental drift. This possibility raises new questions about whether the slab-pull force or mantle-drag force is the primal driving force for plate motion and continental drift.