...Flat slab subduction
           (... is the Nemesis of Plate Tectonics and spells its demise...)

Fig. 1.  Seismic tomography beneath the Japan Trench.  Showing FLAT SUBDUCTION.  No sinking here...   The  'subducting slab' (blue/ cold) is simply being "pushed"  under the continental margin of Japan by the force of ridge-push.  (Vertical cross section beneath Japan produced from GAP-P1. This is the same figure as Fig 2 (a) in Obayashi et al., 2006.)

 
Plate Tectonics would probably say, "Well of course, only a fool would think the cold descending slab sinks into the mantle the way we've been showing it for years and years and years.  *THAT* angle is only the TOP of the going-down part in the upper mantle, ..you know, the lithosphere, ..the brittle bit where you get all the Earthquakes.  Now we know that what *really* happens is that the slab gets pushed flatly under the continents just so far, by the force of ridge-push (..you know, that ten centimetres of dyke that gets intruded at the ridge every year? ...the one forcing the ocean floors apart and pushing it across half the world? ... yes, that one), then it snaps off and sinks (flatly) allowing the part just emplaced to be overridden by the next length of subducting slab.  As it heats up it becomes less rigid (pale blue).   We've been telling you all along about FLAT SUBDUCTION,  haven't we?  So, ..well, ... now it's clear that is what we're dealing with - flat subduction.  We've known all along that the other subduction is really a bum steer, but this one's a little beauty.  Because we thought of it."

"But didn't you think of the other one too?"
"Well, ...Not me, ..I didn't think of it.."

.... So that in time we have a whole lot of them, all stacked one on top of the other descending 'flatly' into the mantle.  You see all those concentric, flatly orientated, pale-blue pixelated layers going right to the core-mantle boundary?  Well, they're all piles of flat slabs, all heaped one on top of the other, going down, zig-zagging into the mantle, ..getting heated up as they go down, which is why they're paler blue, not so brittle you see....

"But some of them are paler than others, and they're *above* darker blue ones.  In fact the one right at the bottom is the darkest blue of the lot."
"Well obviously that's because it was even darker blue to begin with.  You're obviously not getting what this science is about, are you."
"But it's even darker blue than the ones at the top.  Well, the ones underneath the asthenosphere."
"Obviously you need to read a book."

That's what's good about Plate Tectonics, it can be bent any way at all.  It's as bendable as whoever is bending it is bent enough to be bent on making up bent explanations.  It is no more than sheer invention - a bent invention unto whoever bent takes it upon themselves to bend.

Rubber numbers.

But how did we ever get the picture of steep 'subducting slabs" in the first place, when tomography shows it so obviously flat?  Why? Because only ever shown was the edge effect down to about 600km, i.e., what happens at the broken edge between the continental lithosphere and the oceanic lithosphere, i.e., the upper mantle effect. Usually the bottom part is carefully trimmed off in case it spoils things.  There was a story going around, you see ...about how subducting slabs drive Plate Tectonics, so only ever shown was the data to support it, the steep bit returning to the mantle.

But now, with the spin-related, concentric structure of the mantle  becoming ever more obvious through mantle tomography, this concentric, non-descending structure of the mantle slabs is becoming something of a celebrity.   Celeb Tectonics.  (Celebtonics.)

Of course  'flat' slab subduction is a contradiction of the spirit of original meaning of the term,  but what does that matter when there's a whole new gravy train of publication opportunity revving up, just waiting to leave the station.  All Plate Tectonics has to explain now is how the subducted slab (flat subducted or no) gets colder (bluer) as it goes down, as in the figure.  And why the non-oceanic/ continental lithosphere is all hot on the landward side.  Well, we could say that's easy, is it not?  The friction of the slab going down and getting pushed along heats everything up and makes it rise, just like at the ridge, ...even melts it and gives volcanoes.  But the slab of course must stay cold because it has to sink to drive everything, but there are surely research opportunities there too, to pad out this gravy train.

I wonder if this flat slab grinding away underneath the continents, melting everything and making it rise, rises with the rise too...   Or does the slab stay cold while the friction it generates heats everything else up?

You can see from the figure it only gets cold when it meets a continental margin.   If there were no continental lithosphere to force the mantle down there would be no convection and no Plate Tectonics.  It wouldn't matter how hot the Earth was inside, with no continental lithosphere to push the mantle slabs down there would be no Plate Tectonics. (Got it?... the logic of the subducting slab against a continent? .... just by sitting there doing nothing the continental lithosphere is driving Plate Tectonics.)

Now, ..that's the Western Pacific.  It's the same in the Eastern Pacific where the Americas are overriding the Pacific plates.  And it's the same under the Tonga trench.  And it's the same for India, now that it's not India colliding with Asia and crumpling up the Himalayas, but the Himalayas that are being bodily uplifted by India being driven (flatly) underneath causing the collapse of the Himalayas southwards over the Indian Craton.

So with all this so-called "flat subduction" going on (a contradiction in terms if ever there was one) where's the subduction that returns stuff to the mantle to drive Plate Tectonics actually happening?  (Hey, ..More research!  Who said this Plate Tectonics stuff was boring??  Don't you just  luv-vit?)

"Flat subduction"  Googles about 2,860  (0.44 seconds)   June 3rd, 2008
"Flat subduction"  Googles about 7,840  (0.30 seconds) March 08, 2010.
 

Gee, this flat subduction is just crying out for research. That's more than thirty years ago since it started. There's a wiki entry on the web too for just about everything to do with Plate Tectonics, but still no Wiki Entry for flat subduction (as at June, 2010).  How come?  The tomography depicting flat subduction is becoming more and more apparent, and has the potential to torpedo Plate Tectonics in its entirety.  Could this possibly be the reason nobody wants to deal with it (except here)?  Subduction in its various guises is the central pillar of Plate Tectonics after all, ..and 'flat subduction' is its nemesis.

 

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