Continental drift: Where are Africa's subduction zones?

[preearth]

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This is part of a thread from the AWFUL

http://www.bautforum.com/

(i.e., the very, very, Bad Astronomy forum).

Where are the subduction zones for Africa?



The quote;

"The above picture has many features that are problematic for the current theory of continental drift. For example; How can Africa be drifting east, away from the mid-Atlantic ridge, and west, away from the Indian mid-ocean ridge, at the same time? How is it that Africa is also drifting north, away from the Antarctic mid-ocean ridge in the south? Where are the subduction zones? Why are the only subduction zones found in the Mediterranean, which is to the north? How does all this spreading, east and west, end up being subducted in the north? And, why is the region of subduction zones so small, in comparison to the region of spreading ridges?

The Antarctic continent is an even more extreme example of these problems. I will not dwell on the many problems of the current theory of continental drift, but wish to point out, that the reason the African plate appears to have expanded around continental Africa, and the reason that the Antarctic plate appears to have expanded around Antarctica, is probably because they did."

from http://preearth.net/ asks; Where are the subduction zones for Africa?

So,... where are they?

This is an honest question. I have no idea where they are supposed to be.

I want to know what scientists actually believe.

I want to know what the scientific establishment believes to be the case.

A link to a few scientific papers, and/or the attaching of such papers to this thread would be fine.

A "moderator" closed the previous thread

http://www.bautforum.com/showthread.php/105487-Where-are-the-subduction-zones-for-Africa-(the-topic-concerns-continental-drift)

without providing a scientific paper or link to such, while claiming the patently false "everything was answered." And even if everything had been answered, why is that a reason to close a thread.

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[preearth]

How about you explain to us why you think Africa must have subduction zones around it?

The only reason any of us can think of is that you think that a growing africa plate implys a growing total surface area for the Earth, meaning that the Earth's volume must be increasing. That is why we have responded with the subduction being on the other side of the planet in the Pacific. If the Pacific plate is shrinking as fast as the Africa plate is growing, then the total volume of the Earth is constant and things are hunky-dory.

You ain't no geophysicist. That's for sure. More of a magician.

Of course, the surface area is the problem.

A problem that you mystically make disappear by slight of hand.

Consider the mid-Atlantic ridge.

Circulating either side of the ridge are (supposedly) mantle currents.

The currents rise at the ridge and extend away from it for some distance until they descend to the depths and then rise again in a gigantic circulation.

Now the mantle currents fix the mid-Atlantic ridge.

The ridge is a fixed line (really a curve or feature, but lets call it a line) on the globe and cannot drift willy nilly as you are assuming.

Similarly, the mid-oceanic ridge of the Indian ocean is fixed by the mantle currents mechanism.

Consider the mid-Atlantic ridge as a line on the left.

Consider the mid-oceanic ridge of the Indian ocean as a line on the right.

Near each of these two fixed lines, and interior to them, you have millions of square kilometers of new surface being created.

Without subduction the extra area cannot be destroyed and the surface area of the Earth must increase dramatically, which cannot happen without an increase in volume, or something even more spectacular.

The reason you have "no problem" with all this is because you allow the ridges, in fact, the whole mantle currents mechanism, to drift.

You allow the machinery that causes drift, to itself drift.

What mechanism do you hypothesize to allow this drift of the drift machinery?

Of course, it is a nonsense to allow the drift machinery, to drift.

So,... do you now see why one expects subduction?

[preearth]

Why do you think they can't move? They are just convection currents in a fluid. Why would you expect them to be stationary?

If say, the mid-oceanic ridge of the Indian ocean moved away from the mid-Atlantic ridge, then the volume of the two circulating cells between the ridges will have dramatically increased. Something even you would probably agree, ain't gonna happen.

If you can explain (without subduction) where the extra mass to fill the volume comes from, then go for it.

[preearth]

Or then again, probably not. We have atmospheric patterns of high and low pressure where large masses of air move up and down by convection. These are not stationary, so I fail to see why you would expect similar phenomona in a different fluid not to move as well. Obviously, there are difference in things like viscosity and temperature differential which will chnage the behaviour somewhat (the timescales are much longer than for weather, for example) but the basic idea is the same.

Reduced to arguing by vague analogy, I see.

"We have atmospheric patterns of high and low pressure where large masses of air move up and down by convection."

However, the main drivers of weather are large masses of air circulating horizontally. No one claims that mantle currents circulate horizontally. So your analogy is bound to be a poor one.

Then,... Thread Closed.

Discuss all this below.