A new study led by geophysicist Anne Hofmeister at Washington University proposes that imbalance forces and torques in the Earth-moon-sun system drive circulation of the whole mantle.
The new analysis is contrary to the hypothesis that the movement of tectonic plates is caused by convection currents in the Earth’s mantle. Convection involves buoyant rise of heated fluids, which Hofmeister and her team argue does not apply to solid rocks. They argue that force, not heat, moves these large objects.
Even mantle convection believers recognize that the amount of internal heat-energy is not sufficient to drive large-scale tectonics. And there are other difficulties with using convection to explain observed plate motions.
Instead, Earth’s plates could be shifting because the sun exerts such a strong gravitational pull on the moon that it has caused the moon’s orbit around the Earth to become elongated.
Over time, the position of the barycenter-the center of mass between the Earth and the moon-has moved closer to Earth’s surface and now oscillates 600 km per month relative to the geocenter, Hofmeister said. This causes internal stresses, as the Earth continues to spin.
“Because the oscillating barycenter lies ~4600 km from the geocenter, Earth’s tangential orbital acceleration and solar pull are imbalanced except at the barycenter,” said Hofmeister. “The planet’s warm, thick and strong interior layers can withstand these stresses, but its thin, cold, brittle lithosphere responds by fracturing.”
These two independent stresses create the different plates observed in the outer shell, the authors suggest. The variety of plate motions is caused by changes in size and duration of the imbalanced gravitational forces with time.
https://phys.org/news/2022-01-sun-moon-plate-motions-imbalanced.html