上部マントルの非定常熱対流と造構作用 (II)

抄録

Unsteady mantle convection is studied as a continuation of the previous paper (Part 1). Thermal interactions between the crust and the upper mantle are our main interests.
Numerical calculations are performed until a reversal of the initial temperature distribution is realized. Variations in isotherm, speed, stress and heat flow through the Moho are obtained. The speed increases exponentially and reaches the order of 1cm/year. The stage of the maximum stress comes 3-4×10⁷ years earlier than the stage of the maximum heat flow. The former stage may correspond to epiorogenic submarine volcanism (formation of fractures) while the latter to plutonic activity (formation of granitic batholiths).
Considering the time scale of actual tectogenesis (-10⁸ years) and the reasonable range of convection speed (<10²cm/year), the mean viscosity of the upper mantle is estimated as 10²¹-10²² poises. After the convection is grown sufficiently (>10^-3cm/year) the thermal state of the crust has no effect on its subsequent development.