....Where two Plates meet...
           (...There spells deceit...)

<image showing the crust forcing the mantle down - or not...>

Sadly, ..the citation above is true, ..for the ability of Plate Tectonics to explain anything about the processes we see in the geological record are zilch, and so correspondingly is its strength.  For "subtleties" read "everything that Plate Tectonics cannot explain", and the bit where it says "...but Plate Tectonics is truly the foundation upon which the science of geology is built" ... says it all:- geology is in a parlous state.

It is nothing if not ironic, that the glowing tribute to Plate Tectonics above may be read sceptically, for when examined closely, from go to wo Plate Tectonics explains absolutely nothing about geological process.  Nothing at any rate that is in any way credible or sensible.  And in attempts to understand the mentioned so-called "subtleties" of Plate Tectonics, the goalposts of Plate Tectonic theory have shifted numerous times, the most recent shift being that it is the passive flotational properties of the continental lithosphere itself that drives Plate Tectonics.  If you think that's dopey, so it is.  It's like saying that when you're in the bath (which is where children learn all about flotation before graduating to convection and 'porridge' and 'soup' at the table) all the rubber ducks and boats and sponges and other floating paraphernalia set up convection in the water, which drives the flotsam apart.

Of course it isn't stated quite so baldly as that.  Science has to be couched in respectable terms after all.  But that is precisely what its logic boils down to.  And it doesn't take much to pin it to the canvas.  Watch, ..we let them speak for themselves:-

"In a 1962 paper entitled "History of Ocean Basins," Harry Hess, a geologist at Princeton University proposed that the mid-ocean ridges marked regions where hot magma rose close to the surface. Further, he suggested that the extrusion of magma at the ridges pushed the ocean floor away from the ridges like a conveyor belt. In deep trenches like those found off the coast of South America and Japan, the spreading ocean floor was forced down below the thick continents into subduction  zones.  Hess's theory of "seafloor spreading" offered a compelling driving mechanism for Wegener's continental drift, but it needed more proof."
http://www.visionlearning.com/library/module_viewer.php?mid=65

"Forced down"?  But there is no forcing, and logically there can be none.  In continental crust which can be much more easily studied than the ocean floors, suites of intruding dykes are well recognised as passive infilling of dilational cracks.  Oceanic spreading ridges are dominated by the extensional structure of the ridge rift.  And if the ridge is dilating (due to "slab-pull" then there is no justification (and no need) for postulating forceful intrusion.  Magma emplacement at the ridge is gap-filling, and has no capacity to 'push', and besides, from what is known of black smokers at the ridges, 'forcing' would be relieved by magma extrusion.  So, if that was what was meant by 'forcing' during the sixties, what, precisely, is meant by "forcing down" (into subduction zones) today?

Here we have to refer to the current consensus view which is taught in present-day educational institutions.  And it is here we find them (speaking with a single voice,  pinched between a rock and a hard place)  - exactly along lines above - that when two plates meet, the thicker (floating) continental lithsophere forces the thinner denser oceanic lithosphere down.

Does it?  Do boats sit on the fluid ? ..or in the fluid?  It doesn't much matter (as submariners know) since the idea is that it receives an upthrust (equal to the weight of the fluid displaced). The next bit doesn't even much matter either really (if according to that bit we learn in physics about forces - "to every action there is an equal and opposite reaction" is true):-  is the mantle pushing the crust up, or is the crust is pushing the mantle down?  The point is, it's what Plate Tectonic's consensus, to a man, says:-  "The oceanic lithosphere pushes the continental lithosphere up and the continental lithosphere pushes the oceanic lithosphere down".  Especially where they meet - the continental lithosphere will push the oceanic one down.  Don't ask why the continental lithosphere doesn't push the oceanic lithosphere down around the Atlantic - Indian - Southern Oceans, ..that is something to do with the confusion between historical geology as it used to be (which differentiated between the crust and the mantle on compositional grounds), and geology as it is now, which has become usurped by geophysics which differentiates Earth shells on seismic grounds.

It's the next bit that's the real doozy, ...which is that once the oceanic lithosphere is forced down, then, being colder (and denser) than the hot stuff down there (..no it doesn't get warmer and float back up), ..it sinks, ..and sets up the dynamics that drive Plate Tectonics:-
 

"Professor Seiya Uyeda (Tokai University, Japan), a world-renowned expert in plate tectonics, concluded in his  keynote address at a major scientific conference on subduction processes in June 1994 that "subduction . . . plays a more fundamental role than seafloor spreading in shaping the earth's surface features" and "running the plate tectonic machinery." The gravity-controlled sinking of a cold, denser oceanic slab into the subduction zone (called "slab pull") -- dragging the rest of the plate along with it -- is now considered to be the driving force of plate tectonics."
http://pubs.usgs.gov/gip/dynamic/unanswered.html

"With Seiya Uyeda Don (Forsyth) carried out the first formal inversion of tectonic plate speeds for the forces that contribute to plate motions. That work demonstrated clearly that plate speeds are controlled by plate subduction, and that the driving force of sinking lithospheric slabs is nearly fully opposed by resisting forces at overthrust plate boundaries and viscous tractions on the subducting plate." http://www.geosociety.org/aboutus/awards/05speeches/day.htm

Some Pterologists think they can improve on this nutty state of affairs by attributing sinking of the slab to its conversion to its denser material equivalent, eclogite, and say (about the sinking), "Ah, that's because the descending basaltic slab converts to a denser material-equivalent at that temperature and pressure.  It becomes eclogite (denser) and sinks.  As the slab descends through the eclogite transition it gets denser and so sinks".  You're not supposed to ask, "How ? ... If both the slab and the matrix mantle are of the same composition and at the same density and pressure at that depth, why does the slab part sink?"  Well, ...you could ask I suppose, ...but you would be met with the original nonsense:-  "Because the continental lithosphere keeps pushing the slab down, ..the oceanic lithosphere keeps coming along (at fingernail speed) (because dykes are being intruded at the ridges, ..half a world away)  and the continental lithosphere keeps pushing it down".

And there we have it. Once the slab is sinking, it (supposedly) pulls the plate behind along with it, and everything 'convects'.  The plate pulls at the ridge, dykes are intruded, and the convection engine trundles around.  If you can't sort out which has the priority in this 'push-and-pull' convection engine, then you are not alone: neither can Plate Tectonics, and you have an insight into the ridge-push - slab-pull aformentioned "subtlety" of Plate Tectonics, which has all options covered - even the most stupidly contradictory ones.  Being career artists, this doesn't faze Plate Tectonicists one bit, since they know that if anybody protests officially (through attempted publication) the headkickers of consensus will look after them.

What?  ..on the one hand the thermal conductivity of the mantle is supposed to be such that the slab stays cold enough to sink?  ...but on the other hand gets hot enough to go through a phase change?  (Another nuttlety (nutty subtlety) of Plate Tectonics.)

So, ..do you get it? ..."Forcing down".  The subducting slab drives Plate Tectonics.  And this all happens because the (lighter) continental lithosphere is pushing the (denser) oceanic lithosphere down.  That is, ..just by sitting there completely innocently, ...doing absolutely nothing besides just being there, ..the continental lithosphere is causing the Earth's crust, that is, itself, ..to break up and be crumpled and crushed to Kingdom Come!

I mean, ..is it me?  Or is it them, ..is dopey here?

(This is tiring me out...  )
 

 
 

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