On the dynamical theory of polar wandering

Abstract

A new approach to the dynamical theory of polar wandering and continental drift is outlined. This prospectus bases on the following hypotheses: 1. (1) The earth's outer shell, particularly the rigid lithosphere, is irregularly fractured, and the hypothesis of continental accretion is accepted; 2. (2) the earth's outer shell is heterogeneous, multilayered, and has low thermal conductivity, and there are lateral temperature variations in these layers; 3. (3) the hypothesis of mantle-wide, regular and cyclic thermal convection in the earth is rejected, and the asthenosphere-wide convection hypothesis is preferred; 4. (4) the generation of thermal energy in the earth is, or has been in excess of the energy removed by the surface heat flow; and 5. (5) the temperature at the earth's surface is approximately constant in time, and the earth's outer shell has never been “totally” molten since its formation. The outer shell refers to the uppermost 700 km layer of the earth with the upper 60 km as the lithosphere and the rest the asthenosphere. The thermoelasticity of the earth is briefly reviewed, and the thermoelastic energy storage in the outer shell is estimated as of the order of 10 35 ergs or higher, which is in conformity with the amount of excess thermal energy that may be accumulated in the earth during a geologic epoch. As the thermoelastic energy accumulates, the stress levels of the multiple layers in the outer shell rise accordingly, with differential expansion following. Within a geologic epoch, the stress difference in the lithosphere would reach its critical value, meanwhile the accumulated energy would also produce melting in the upper asthenosphere and then induce drastic changes in physical conditions to the surroundings. Because of the rigid, fractured and multilayered nature of the outer shell, catastrophic failures would occur before the upper asthenosphere was totally molten. These gigantic failures represent the major release of the disequilibrium energy in the earth and would occur repeatedly as the excess thermal energy continues to accumulate; so that all the basic geological phenomena are episodically induced. The immediate effect of the failure would be the excitation of polar wandering and a short-lived wobbling of the figure axis about the rotation axis, which might consequently produce torsion on the earth. The failure would also produce a torque on the earth which would force the lithosphere blocks to slide slowly over the asthenosphere relative with each other and thus result continental drift, orogenesis, epeirogenesis and other related phenomena. In the meantime, intense extrusion and intrusion of molten materials from the upper asthenosphere might immediately follow, which would “seal off” old geofractures and thus enlarge the continents. The after-failure tectonic activity would last a long time and a large amount of energy would thus be consumed. As the accumulated disequilibrium energy in the earth was greatly released, the earth would gradually return to its relatively quiescent period but, in the meantime, new energy accumulation would proceed for the next diastrophism. By and large, this dynamical prospectus may serve to interpret almost all the major geological puzzles observed.