.....Plate boundaries - 'moving' plates
           (...Plates and plate boundaries, ..the knot that Plate Tectonics has tied itself in... )

Fig.1.  The conundrum of 'plates'.  Plates move, but their boundaries don't?  Just as water passes beneath the window of a glass-bottomed boat, so the oceanic lithosphere is supposed to move beneath the boundaries of lines depicting plate boundaries on plate maps. (Blue = oceanic lithosphere; red = 'window'/ plate boundaries on plate maps; arrows = pull of subducting lithospheric slab.)

 

Plate maps are seriously misleading because they don't really show *plate* boundaries at all, ..at least not in the sense of segments of the Earth's crust ("jigsaw pieces") that move about on the Earth's surface,  ... i.e., "pulling apart", "colliding", and "grinding past" each other. What they do show are immovable lines inscribed in the lithosphere whilst the lithosphere itself (supposedly) moves.  Thus the Americas and Africa (say) (chunks of continental crust), have moved from the Atlantic spreading ridge to where they are now, ... ferried on the back of a convection cell, ..namely the ocean floor we see today.  That is, the ocean floor has 'moved'.  But its boundaries haven't.

"How can this be?", you might ask. "How can the lithosphere move without the lines inscribed in it marking so-called boundary segments moving too?"  Well, the short answer is, they can't.  And they don't.   It's a contradiction in terms, raising the question, "What exactly is a plate?", and "What (therefore) is a plate boundary?"  And, "Hhow, therefore do these 'plates' (with boundaries) move?"  It's rather like saying the plate boundaries are the margins of a window fixed in the floor of a glass-bottomed boat which is anchored and doesn't move, while the 'current' beneath, i.e., the lithosphere does. Movement enters from one side (the spreading ridge) and exits the other (pulled at the bend-down of the subduction zone), whilst the window itself (the plate margins) stays fixed.  In other words, the plate boundaries are in the window which is fixed in size and position, but the movement is in the water beneath.

'Plates move, but their boundaries don't' ...  is certainly a most curious way to depict how the broken parts of the crust "collide", "grind", and "move" past each other.  One might as well say (alluding to vascular circulation or digestion) that one is moving on account of internal 'convection'  even whilst sitting still.  Certainly we can talk about the crust as the top of the plate moving, and we can talk about the lithosphere of the entire crust plus upper mantle moving, but not the plate itself as defined by its boundaries, moving.   As Plate Tectonics stands, the 'plate' is something apart from its boundaries.

Virtually by Plate Tectonics' own definition the paired boundaries of spreading ridges and subduction zones cannot move; for if  they did then they would have to move in the same direction and at exactly the same rate for the Earth's surface to maintain a constant size.  And there is no evidence that ridges (at least) move in this way.  The only way Plate Tectonics can maintain its position is to say that plates came into existence already formed at their present size and location - which is also a nonsense.

The reason for this peculiar state of affairs is a clash between traditional geology which discriminates between crust and mantle on compositional and general geological grounds,  and the more modern field of geophysics which does not, but discriminates simply the outer brittle shell of the Earth (be it crust or mantle) according to the distribution of earthquakes, and which has coined the term 'lithosphere' to define this combination of brittle (on account of earthquakes) crust and upper mantle.

However there is complication here too following from the actual distribution of earthquakes.  These occur in two markedly distinct zones - the spreading ridge and the subduction zone.  At the spreading ridges earthquakes (i.e., by definition lithosphere, ..i.e., crust + upper mantle) reach to a depth of some 6-12km.  At the subduction zone earthquakes reach to a depth of at least an order of magniture greater, 600-800km, ...on occasion up to 1000km, i.e.,  well past the depth regarded as upper mantle.  Here, 'crust' is rather a misnomer, because these earthquakes occur not in the crust (as geo-logically defined), but at the interface between continental ltihosphere and oceanic lithosphere, reaching below the upper mantle and well below the 20-40km superficial thickness usually designated 'crust'.

There is a further complication in that both are zones of brittle deformation which describe correlative movement, i.e., movement at one side (the ridge) is matched with movement at the other (the subduction zone) even though the sides themselves (the 'plate margins' described above) do not move, yet the part in between which is the 'plate' proper and which is supposed to move has absolutely no seismic activity at all.  Seismically it's as seismically dead as a dodo!

What? The plate margins which are inscribed on the Earth's surface and which do not move are seismically active, but the main body of the plate itself - the vast expanse of ocean floor - which does move (is supposed to move) is seismically dead?   How is that?  Plate Tectonics is apparently quite happy to match the earthquakes of the spreading ridge with those of the subduction zone on grounds of plate 'movement', and yet the great expanse of ocean floor in between which is supposed to move is seismically dead?  It's a nonsense.

The only way this seismic silence of the ocean floors can be explained is in fact if they are just that - dead as a dodo! - in other words,  the plate is not moving away from the ridges at all, but the ridges are moving (or rather 'growing') away from the continental margins leaving a 'dead zone', a zone of inert, fossilized ocean floor in their wake.

But the ridges manifestly do not move on the Earth's surface.  Equal spreading on either side of the ridge precludes it.  So we are left with the inescapable conclusion that the only way the ridges can 'move' in this way (but not move east west north or south), is if they 'move' UPWARDS, so necessitating areal movement as a corollary.  That is, movement in two dimensions is apparent only, consequent on real movement, which is in the third dimension, ..upwards, ..outwards from the Earth's centre; ...i.e.,  the continents are fixed, and only appear to move apart as the ridge moves upwards.  Well, ..of course they move relative to each other, ..but not to their basement: they are fixed to their basement.  Which is why the crust-mantle boundary beneath the continents is so difficult to fix and why the continents are said to have "deep roots"

(Googlesearch <continents "deep roots"> = results of about 11,100 for <continents "deep roots"> ).

Thus the  200km mantle thickness of of strong seismic activity at subduction zones is logically not at all paired with the seismicity at spreading ridges in the way meant by Plate Tectonics, ..these two seismic zones actually represent different things (as described on this site) - nothing to do with "moving lithosphere".   (And just briefly what are they?  Well, the ridge represents mantle growth; the so-called subduction zone represents accommodation of the pangaean hemispheres.  That's it, in a nutshell.)

So, ..having defined plates as  'lithosphere' (upper mantle + crust), and recognising that lithosphere is 200+km thick at subduction zones and extends down to around 800 - 1000km,  Plate Tectonics is in the position of having to represent the boundaries of plates (lithosphere) (i.e., the plates we see on a map) using only the visible crust.  It attempts to do this by distinguishing 'plate' (the flat part of the ocean floors) from 'slab' (the going down part) (Figure above), and scribing the line on the bend between them, but it is really in a no-win position. Scribing lines on the surface of the crust does not define 'plates' as Plate Tectonics needs them to be  Segments of crust appearing to move whilst plates do not is hardly justification for talking about "moving plates" - i.e., lithospheric margins that are fixed whilst the lithosphere moves through them -  ...and not even through them, but beneath them.  It is Plate Tectonics own definitions which have led to this conundrum, and which has led the Geological Society of London to deplore on the way this has carried through to the erroneous teaching of Plate Tectonics. However it is merely pointing out a deficiency in logic, not offering any solution to the conundrum.

The short of it is that Plate Tectonics is exactly that -  a depiction of two-dimensional global geology, whilst in reality, ..and implicit in Plate Tectonics' own definitions the major features of the Earth's crust are manifestly a result of dynamics in the third dimension - outwards movment from the centre.   Up and down.  Which is what the crust of an expanding Earth does: moves up here and moves down there as the crust accommodates the enlarging surface of the Earth.  Plate Tectonics on the other hand negates this up and down movement, relegating it to second place in importance of the created dynamics as the 'plates' "move, slide, collide and grind past each other" - in two dimensions.
 
 

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