....Subduction - the crux of Plate Tectonics

Fig.1.  Two standard templates for subduction.  We need go no further than these images, in conjunction with the emerging evidence for Flat Subduction, to know that Plate Tectonic theory is fatally flawed and bears little resemblance to reality.

 

Subduction is the crux of plate tectonics.   It is the lynchpin on which Plate Tectonics depends for without it the mantle would simply be extruding with no compensating correction. And the planet would therefore be getting bigger.

It is important to recognise the essential role that subduction plays here.  Plate Tectonics is not to do with the separation of the continents, nor anything to do with the creation of the ocean floors, spreading ridges, transform faults, nor indeed the differential overriding/ underthrusting movement on the subduction zone, ...for all of that is about the Extrusion of the mantle and the Earth getting bigger - which is the nemesis of Plate Tectonics.  Plate Tectonics is specifically about the actual underthrusting of  oceanic lithosphere and its return to the mantle, for it is this that maintains the areal balance of the planet and the integrity of Plate Tectonics.  Without subduction 'Plate Tectonics' would in fact be Earth Expansion.  As the crux of Plate Tectonics, .. Subduction Rules.

Of course, because subduction *is* an assumption (and a convenient one) doesn't mean to say it is wrong. It could be right after all.  It's just that there are as many elements of contradiction as there are elements of support. So which are to be believed?  The crust floats on the mantle?  No, the crust (lithosphere) forces the mantle (oceanic lithosphere) down.  The colliding plate pushes up mountains by crumpling the crust (as in the type area of the Himalayas)?  No, the colliding plate slides underneath the other and lifts it bodily upwards with no crumpling (as in the type area - again - of the Himalayas).  Continental crust cannot subduct? Yes it can (if it happens to be India, ..sliding under the Himalayas to lift them up) (or any other piece of continent - like Africa, colliding with Europe to 'crumple' the crust and throw up the Alps (even though the Mediterranean sea between Africa and the Alps is an extensional basin and the fold structures are manifestly gravitational collapse structures,  not 'push' structures.   The subducting plate ('slab') sinks because it is cold and therefore more dense?  No, it sinks because it is being forced down when it meets the continental lithosphere.  (which is floating on it).  The subducting slab pulls the ocean floor down with it?  No, the ocean floor is being pushed from the ridge ("ridge-push").  Of course in this instance of contradiction if both were to operate, as Plate Tectonics says - as"slab-pull ridge-push", then there would be accellerating runaway dynamics that would be tantamount to more than a perpetual motion machine.   And no, it is not like the pull-and-push of a freight train, with an engine at the front and one at the back, because in the freight train example the power units are independent; in Plate Tectonics' reasoning the push of the following engine (ridge intrusion) is powered by the pull of the leading unit.

Pull at one end generates push at the other?  Rubbish.   But in the name of 'convenience'  this inconvenient logical glitsch is simply overlooked.  Likewise the notion in general of Plate Tectonics being driven by the subducting slab.  It is a mighty subducting plate indeed that pulls the Earth's crust apart in two places at once - back-arc basins on the right (in the lower figure), and the spreading ridge on the left , ..the latter more than half a world away across a terrain that geologically speaking has little more cohesion than rubble.  And clearly (if subduction is the driver for Plate Tectonics, which is the current view) then the spreading ridge would stay where it is and the ocean floor would grow only on the subducting side.  How one subducting slab balances with the other on the opposite side of the ridge half a world apart to maintain ridge symmetry and equalise spreading is not even addressed in Plate Tectonics.

 
Let's continue, shall we?

The subducting slab grinds down the subduction zone causing frictional partial melting which makes its way to the surface as volcanic extrusions (the Fiery Ring of the Pacific)?  No, it falls vertically, causing rollback of the down-bend and pulling off chunks of continental crust to form back-arc basins ("blobtonics"), and thus, in free-fall - like the Titanic - driving Plate Tectonics.  The falling slab pulls on the ocean floor from the ridge?  No, roll-back means there is no pull on the oceanic plate, ...the pull of the slab terminates on rollback - all the way back to the spreading ridge; the slab falls, and the line of mantle turn-down 'rolls back').   Convection is driven by the heat of the Planet's interior?  No, it is driven by coldness of the falling slab.  The slab is cold and falls?  No, being cold is not enough.  It has to get hot enough to convert to its denser equivalent, eclogite before it can sink.  Older dense slabs sink faster than younger lighter ones?  No "dense plates tend to be held in the upper mantle, while younger and lighter plates sink more readily into the lower mantle" <link>.)

Transform faults are expressions of slow ductile mantle flow?  Mmm, theoretically they are, but in fact no, they are brittle faults with earthquakes.  The Earth's crust is segmented into a number of plates?  No, beyond the short distance from the ridge where earthquakes (fault movement) occur the ocean floors on respective sides of the ridges the entire ocean floor is locked as one across all transform 'faults' (fractures).  Thus there are no 'plates' moving 'independently' (another point that Plate Tectonics conveniently ignores)  Even in Plate Tectonics the concept of 'plates' only has relevance in the immediate vicinity of the ridge, yet we are supposed to accept plates as separate independent entities moving this- way- and- that across the entirety of the planet's surface.  And for the history of the planet.

So, in view of all the above contradictions we have to ask how did it ever come to a pass that subduction ever gained such acceptance, when it is tantamount to little more than a convenient lie?   What was it shoring up?

It was shoring up a false assumption - that the Earth could not get bigger (because there was no known way in the current understanding of physics theory that it possibly could), ..when empirically it clearly had - by the amount of the ocean floors; obvious in the region of the Atlantic Indian and Southern Oceans, ...not so obvious in the Pacific.  It was this apparent lack of a continental fit across the Pacific that edged structural interpretation closer to interpreting Pacific continental margins as subduction zones, where the oceanic crust (/lithosphere) was  being returned to the mantle.  However with the resolution of this problem according to the reconstruction on this site  the whole justification for 'subduction' as the crux of Plate Tectonics.has been removed.  Geophysical theory can say what it likes of subduction, but both empirically and conceptually, in the piecing together of the geological facts, it provides no justification for Plate Tectonics.
 

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