My science/technology-related thoughts, sometimes controversial, sometimes can be based on limited knowledge base, logic can be non-perfect as well. I develop my vision in iterations. Don't take this blog as an attempt to convince anybody in anything.
Each post in this blog reflects my level of understanding of Tectonics of the Earth at the time the post was written; so, some posts may not necessarily be correct now.

06 May, 2011

Plate Tectonics. Thinking Out Of The Sphere.

A problem with plates "floating" on the asthenosphere.

Wegener thought that the continents were moving through the earth's crust. Now the mostly accepted point is that continents do not move through the ocean floor. Rather, continents and oceanic floor form solid plates. And the plates move over the asthenosphere, the highly viscous layer of the upper mantle of the Earth.

But, really, don't you see the problem with the approach: a plate floats over the viscous layer, which floats over just liquid magma? We know some plates reach as far as 700km and even greater depths, and their bottom is not flat. How would such complex structure manage to flow over the highly viscous layer? The viscous stuff is not glued to anything, it would just go with the plate over liquid magma.
Why not to suggest that both parts - solid and viscous parts are drifting over magma?

Wegener suggested that continents drift through the earth's crust, later it was corrected that entire plates "float" on the asthenosphere. Why did the science stop at this point? Why was not it suggested that both parts - solid and viscous parts are drifting over magma? I could imagine two reasons:

- Nobody risked to insist on such "revolutionary" step remembering how Wegener was treated with his much milder suggestion. Taking the step would mean that a plate owns its underlying viscous stuff and moves with it. This would effectively discard the legacy concept of asthenosphere as a physically consistent world-wide viscous layer.

- Science needed explanation how plates move. The underlying viscous stuff was magically decoupled from its upper solid host and it was suggested that the decoupled layer can transform the  interaction with underlying magma into the force to move the plate.  
Avoiding postulates. 

I'd like to suggest that there is no need to decouple plate's underlying viscous layer. Let a plate "own" its viscous layer and move with it. Let's suggest that plates are driven by divergent boundaries as was described in my previous posts. I don't see how the suggested magma transport mechanism contradicts lows of Physics. Though I must admit, right now I can't back my considerations mathematically or experimentally. A quick search reveals that the closest in this direction were research works on shear-driven upwelling. Probably, the proposed mechanism will get attention as well.

If proven that plates are driven by divergent boundaries as was described in previous posts, then we don't need to make highly controversial postulates that feed so well the opponents of theory of Plate Tectonics. For instance, the postulate that oceanic divergent boundaries are made by some mysterious hot magma jets, the jets that don't obey Coriolis effect, the jets that can pump magma up as high as many kilometers.

We don't need to postulate that plates are driven by some mysterious magma flows, and driven not directly, but rather by means of separate world-wide layer - Asthenosphere. Instead, we could assume that everything beneath the plate's upper layer belong to this plate. It's just a)solidified, b) semi-solidified magma or semi-molten another plate subducted under this plate.

Of course, the plate on its way can lose some of its less viscous stuff on its bottom by the process of magma recycling. But on average, due to the Earth being cooled, it gains more by the plates subducting process.

With the help of the theory outlined in previous posts we can explain the oldest parts of plates with the roots as down as many hundred kilometers. These parts had been subducting other plates at the beginning of the plates evolution. As magma is globally cooling, the melting temperature of subducting plates was higher than the temperature of magma of newer ages. The subducted plates just added to the bottom of the oldest parts of plates as a semi-melted stuff. As magma temperature was dropping, the underlying layers of the plates were increasingly solidifying.

A number of other postulates could be avoided as well, but, probably, it can be the subject of the next posts.
New concept of Plate.

Probably, in the future it would not be a bad idea to rethink further usage of the concepts "asthenosphere" and "lithosphere", as the concepts don't fit well the proposed theory. The suggested new concept of Plate, I'd like to define the next layers:

1. Solid layer.
1.1 Upper solid layer - crust, can be investigated by mechanical tools.
1.2 Bottom solid layer, too hot to be investigated by mechanical tools.

2. Transition layer. Here seismic wave speed would undergo, say, 10% to 90% of its speed change.

3. Viscous layer.
3.1 Upper viscous layer, persistent to the plate on the course of, say, 10 million years.
3.2 Bottom viscous layer, participates in magma recycling process;

reposted from
(edited Jun-17, 2011)

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