....Where Plate Tectonics fails ...most magnificently
              (...is in representing overriding as subduction...)

It sure is (a challenge), ..because the essential dynamics of what is really happening at the subduction zone is OVERRIDING, ..not subduction.  It is the crust riding out over the mantle as the Earth gets bigger and its surface curvature relaxes that is the determining mechanism.  Plate Tectonics ascribes this riding out to a feedback convection loop, consequent on a 'sinking slab', like water being dragged over the hull of a sinking ship.  Failure to recognise this scale difference and the consequences that follow from it most certainly results in an "important challenge".  For the goal is an illusion, no less than trying to represent an image in a mirror as reality itself.

It is exactly here that Plate Tectonics fails most magnificently, in pitching geophysical speculation against geological reality, for a geological synthesis puts the active dynamics of what is happening squarely on the continental side of the zone (as overriding), not the oceanic side (as subduction due to convection).  By putting all its cards on its basic assumption, the rubbery arithmetic to support it, and by not integrating the various geological parameters in a consistent way, Plate Tectonics is blatantly demonstrating the hubris of the scientific college  - and trashing Earth science as Junk.

Plate Tectonics is further compromised with the increasing revelation that seisimic tomography is showing that subduction is not the subduction we have been led to believe (the subduction that returns oceanic lithosphere to the deep mantle), but is in fact 'flat' subduction, which gives no convective return to the deep mantle but is linked to a global pattern of spherical tomography that is reflective of the Earth's spin rather than convection, and therefore is far more indicative of the crust (continental lithosphere) 'skating' (or 'overriding') *on* the mantle (asthenosphere) than it is of cycling retun *to* the mantle as advocated by Plate Tectonics.

Plate Tectonics adds smoke to the image by fully acknowledging the importance of overriding, but failing to assign importance to it.

Hedging bets:-  In the best tradition of thieves and robbers the USGS and NASA are 'shooting through' with the nomenclature booty, leaving the Wikipedia holding the subduction baby.  The Wiki - perhaps not the most authoritative on the subject since it is written (and edited) by you and me, but by far the most sincere in adhering to the meaning of the word, ..'sub', meaning 'under' or 'beneath', ... and 'duct' meaning 'carried' (subducted = carried beneath) openly maintains the role of convection in Plate Tectonics.

Not so either the USGS or NASA whose rephrasing of subduction ('carrying' down') in terms of overriding, sneakily allows them to speak with a forked tongue, one fork (the one described by current illustrations on their respective sites) allowing them to maintain the myth of convection, whilst the other fork allows them to position themselves for the next seismic shift in the Plate Tectonic goalposts along lines described on this site, ...that of 'overriding'.

The problem with 'overriding' (for Plate Tectonics) is that it carries no connotation of convection or subduction, and therefore if it goes down that road of enquiry must abandon the whole notion of convection, which with so many convectioneers (geophysicists) at the helm of Earth science would be unpalatable.  Geologically however it is an admirable solution to the questions of crust - mantle  dislocation, which when tagged to the longitudinal symmetry of pivotal opening of the Atlantic about the North polar region, and the so-called 'flat subduction' is clearly related to the Earth's rotation.

So, ..thieves and robbers?  (Something here about that bit about later generations dusting off and claiming as their own the earlier ideas they strenuously rejected, and why real change virtually never comes from within the mainstream.)

Well, ..Possibly, ..except for that other bit about subduction happening where the crust pushes the mantle plate down and the zone of earthquakes being a subducting 'slab' which "drives the Plate Tectonic machinery", ... which reassures us that they really are nuts.

Just in case you're not sure what they're saying here it goes like this:-

1. The crust floats on the mantle (because it's less dense);
2. The crust (which is floating) pushes the mantle down (on subduction zones);
3. The subducting slab (which is not a slab at all but really a zone of earthquakes) drives plate Tectonics;
4. Plate Tectonics is the mechanism causing crustal deformation (crumpling mountains etc).

So, ..just by sitting there doing nothing except floating on the mantle, the crust is causing its own deformation....    On this basis alone (for this *is* the consensus position) any attempt by Earth scientists to get ahead with their smokey mirror image is laughable.   They can steal from reality what they like.  With this rubbish as their core foundation They're sure to end up in jail, ..without even passing 'Go'.  The charge? ...  ceating a false belief, a ploy for which young children, somewhere around the age of four, ..are well known.

(Include quotes here along the lines of NASA and the USGS about the crust forcing the mantle down..) (Fry them. )
(Begin:-)

 
The crust forcing the mantle down?  It's laughable.   But no, they're not joking.  It's the only way in their model that they can rationalise the sinking of "cold slabs" on a line against continental margins.  How else, when it's all hot down there?  Of course it does occur to them that the model might be wrong.  But it's no big deal since everything else they 'rationalise' in Plate Tectonic theory is nonsense anyway.  Wrongness or rightness is not the point.  It's a consensus thing, ...and paying a lot of mortgages.  That, of course, is not  the proper way to express this sentiment. It must be framed in the context of professional competence, so it goes like this:-

Trouble teasing out mechanisms?  Well, no wonder when there is such conflicting opinions as  "It's the continental lithosphere forcing the mantle (oceanic lthosphere) down that drives Plate Tectonics, ...and that "It's the subducting slab itself that drives subduction as the cold slab descends into the hot interior and undergoes a density change from basalt to eclogite"

Get it? - the mantle gets denser because of cooling,.. and also gets denser because of heating as the (basaltic) subducting slab is converted to eclogite.  Another breathtaking example of doublethink by Plate Tectonics.  Evidently it is not supposed to occur to us that this environment must be already of eclogitic composition (such is the temperature and pressure into which the slab is falling), ...and that eclogite into eclogite doesn't go - at least not with any remainder that can make the slab 'heavier' than its surrounds.  Simple division.

Since the only difference here is whether the mantle is at surface and flat (spreading), or going down and steep (subduction), one is left to infer that flatness and steepness are arguably the controls which determine whether the mantle gets denser by heating or by cooling: if it's flat and going along (spreading) then it gets denser by cooling; if it's steep and going down (subducting) it gets denser by heating.   To which the obvious corollary is that if it's steep and coming up (as under a spreading ridge) it gets less dense by cooling.  Which, it could be argued, is why it rises.  Well, why not?  If it can get more dense by heating, surely it can get less dense by cooling?

 
Subduction occurs as the corollary of spreading ridges - with exceptions being all around the Atlantic Indian and Southern Oceans - quite a large slice of ocean margin by any account.  Which leaves the Pacific. But the dimension of the Pacific margin is only about half that of the length of the spreading ridges, which means that the rate of Pacific consumption (subduction) is about twice that of creation of ocean floor, ..i.e., the downward cycle of convection is twice the rate of upwards convection, and even more than that if we consider that the Western Americas are overriding the Pacific rather than subducting.  (Google up "flat subduction" - a contradiction in terms)

Secondly, if the oceanic lithosphere is being returned to the mantle in this way, commensurate with uprise and ridge creation, then the ocean floors would never open in the first place.  Now, ..would they?   The destruction of ocean lithosphere in subduction zones would be simultaneous with creation of mantle crust at the ridges  - and the ocean floors would never open. You don't have to be a rocket scientist to see that!

Thirdly, a couple of hundred or so earthquakes going off every week around the Pacific i.e., brittle failure every day for the last few hundred million years has reduced the brittle crust/ mantle interface here to effectively rubble. It's just shameless asinine nonsense to suggest this pile of dross is a coherent slab that sinks and drags the Earth's mantle crust of the ocean floors around with it as it does so, which is equally riddled with fractures from transform faults and the spreading ridge,

Conclusion:-  On simple prima facie grounds subduction is rubbish.  And with no subduction there is no compensation to ridge creation, and the only bit of Plate Tectonics that has relevance is the emplacement of the ocean floors as the continents separate - which is ... the bit we can see, ..which is, ...  (wait for it), ....Earth Expansion.
 
 

Crazy Platies.  Nuts.  And afraid.  Afraid to venture into the unknown...
....Consensus animals...   Why?

Because in the academic world thinking for yourself is professional suicide.  You stay in your cage and only come out to feed.