CAN OCEAN TIDES DRIVE THE CONTINENTS?

Disproof of large-scale convection cells as a continental driving force has left a void. Convective down-drop at trenches supplies a vertical force, but associated “trench pull” seems too attenuated to be viable across oceans and continents. Here I consider an alternative: ocean tides create an inertial horizontal driving force that acts on the entire planet and explains continental movement in both east-west and north-south directions.

The pull of the sun and moon on the oceans stores and releases energy with a resonance determined by rotational periods and basin shapes. The heights and currents created induce daily and sub-daily oscillations in the Earth’s rotational velocity and axial orientation. And, in turn, the rotational variations induce an oscillating instantaneous global inertial force (Euler force)—a force that can be quite high at its peaks because of the tidal resonance.

At present, VLBI and GPS measurements and computed simulations allow calculation of approximate values for inertial force—values that follow inherent tidal asymmetry and show a net directed force. In addition, asymmetric secular forces associated with zonal tides, subduction, and bathymetric gradients as well as atmospheric effects provide directed forces capable of creating ratchet-like movement of continents over time.

The Earth’s rheology is as important as the force itself. Early assumptions that the mantle is a generalized Newtonian fluid with a viscosity determinable from glacial isostatic rebound and seismic measurements led to a conclusion that astronomical forces are too weak to drive the continents. More recent work focusing on strength envelopes of crust and mantle materials (the “jelly sandwich”) suggests that reduced yield stress between crust and mantle could focus the effect of the inertial force at the crust mantle boundary and produce horizontal movement at lower stresses. Calculations suggest that the horizontally directed inertial force with the noted secular additions may be a sufficient driver.

An ocean tidal driving force promises a coherent explanation of numerous geological and geophysical features including the formation and propagation of rifts where ratcheting forces oppose, apparent movement and anisotropy on mid-mantle seismic disconformities, past changes in drift patterns, and many others.