GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 59-7
Presentation Time: 3:55 PM


HOFMEISTER, Anne, Department of Earth and Planetary Sciences, Washington University, Campus Box 1169, St. Louis, MO 63130, CRISS, Robert E., Earth and Planetary Sciences, Washington University in St. Louis, 1 Brookings Drive, Saint Louis, MO 63130-4899 and CRISS, Everett M., Panasonic Avionics Corp., Lake Forest, CA 92630

Plate tectonics is currently attributed to mantle convection driven by radioactive heat, although this energy source is known to be insufficient. We show that its basis, Rayleigh’s criterion, implicitly assumes (1) thermal diffusivity of the material equals its kinematic viscosity, which describes gas and liquids, but not solids and (2) that the material will flow under any stress. In contrast, solids are moved by forces, not by heating. Gravitational forces move large, remote masses over astronomical scales. Here we describe how plate tectonics, differential rotation of the lithosphere, and the radial drift of the Moon from Earth each arise through imbalances of Solar gravitational pull against centripetal accelerations as the geocenter and Moon wobble about the plane of the barycenter orbiting the Sun in a co-ordinated manner. Earth’s spin about its oblique axis compounds force imbalances on its lopsided lithosphere. The lithosphere is a product of heat production and loss, with magmatism.

The lunar orbit is destabilized by Solar pull on the Moon being 2.2x Earth’s. Eventually, the Sun will capture the Moon, as it likely captured former moons of Venus and Mercury. Earth’s spin is not being transferred to the Moon as popularly assumed, but is internally dissipated via differential rotation, as evidenced by Westward drift of the lithosphere. This chill zone glides on the thermally weakened, low velocity zone. Force imbalances caused by Earth’s non-central barycenter impose a low symmetry stress field on the brittle lithosphere. Daily and monthly cycles cause fatigue, yielding plate tectonics. Subduction is a geologically recent phenomenon, because the chilled lithosphere must be sufficiently thick to prevent re-sorption at shallow depths, and to bend rather than break. Comparing rocky planets shows that the presence and longevity of tectonics depends on the particular combination of the mass of the object, plus the mass and orbital orientation of any moons, proximity to the Sun, and rates of body spin and cooling. Motions depend on force direction. Thus, activity of planets is primarily driven by differential spin and gravitational forces, and is greatly magnified if a large moon is present.

*E.M. Criss prepared this article without use of information, resources, or other support from Panasonic Avionics Corp.