Subduction – Force Problems

Subduction is a process that makes physically no sense. Have a look at the P-wave tomography picture of a presumed subduction zone from Zhao, D. (2001) published in the journal Physics of the Earth and Planetary Interiors:

We see that the blue path strictly respects the oblique section of the continental block. The force of gravity is perpendicular to the surface. One would expect that if the subducting plate had sank down deep into the mantle thanks to gravity, it would have moved with respect to gravity. This is not the case.

For unknown reasons, the plate chooses the path that is adjacent to the continental block. The next thing is that such ‘choice’ results in overcoming the resistance force that is at the continental block/oceanic lithosphere boundary.

The better explanation for the observed relations in the picture would be a simple precipitation/solidification of basalt from the ‘basaltic bath’ at the boundary.

Tonga/Lau Region Experiment

Leave a Reply

Your email address will not be published. Required fields are marked *