Tonga/Lau Region Experiment

‘Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced or sinks due to gravity into the mantle. Regions where this process occurs are known as subduction zones.’ (Wikipedia)

These are the two first sentences from Wikipedia. But one can ask – Does subduction exist? Could the zones be just crustal zones of solidified basaltic material from depth at the oceanic/continental lithosphere boundary?

I decided to make a very simple experiment. I prepared a paraffin wax and created a wooden continental block. The block was inserted into the liquified wax.  The ‘oceanic crust’ was created in few minutes. But the most important part was the oblique section of the continental block. What will appear there?

This is an image of a ‘subduction zone’ via P-wave tomography from Zhao, D. (2001) published in the journal Physics of the Earth and Planetary Interiors:

We see there a sharp contrast between the continental block(s) and oceanic crust (blue color). As been already mentioned, the image should visualize the so called subduction zones, which are presumed parts of Earth where oceanic lithosphere should slowly slide into the deeper parts of the mantle.

My experiment showed that the wax cooling led to a creation of a thin layer at the surface (air/wax boundary – max. 2 mm) as well as at the continental block/oceanic lithosphere boundary (wooden block/wax boundary – max. 1 mm).

The reason for the observed phenomenon is that the wooden block became colder than the inner parts of the wax container.  So the wax could solidify there. The fastest wax solidification was seen at the container glassy walls. If the block was made from another material like glass or granite, we would probably see even thicker layer at the wax/continental block boundary.

I think that the first experimental results represent a very good reason to think about the ‘subduction zones’ in a quite different way, maybe even easier way. I hope that more detailed experiments will follow.

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