A possible mechanism of inversion of the vertical lithosphere movements in the back-arc basins of the West Pacific region

We present results of the study of a three-layer tectonosphere model of the West Pacific Transition Zone based on modeling of a piecewise inhomogeneous medium caused by local density reduction of the asthenosphere, whose viscosity decreases due to fluid accumulation. We used the viscous liquid motion equation in the Stokes approximation. It was shown that the anomalous asthenosphere in the back-arc basins can move as a convective cell with an uprising flow in the zone of maximum density reduction and extension of the lithosphere above it. At the initial stages, this process causes formation of the central crustal uplift, which is transformed into a system of depressions as the asthenosphere viscosity decreases to values of the order of 4.0 × 10¹⁹ Pa s and lower. The modeling results satisfactorily agree with the reconstructions of the Cretaceous Cenozoic lithotectonic evolution of the Okhotsk Sea region.