....Nankai Trough -1
           (...Accretionary prisms as slump structures )

 
Fig.1  Two mutually opposed interpretations from the same seismic data.(a) Slumping (here /above) as Japan collapses into the trench.  A crevasse-like structure marks the extensional breakaway from the top of the slope down which a cascade of gravitational slumps collapse away from the landward buttress (Japan). Piling up at the front of the block is simply a function of curvature correction of the continental crust.  (b)  Crevasse and slumping apparent in the seismic data not incorporated in the figure appear to be ascribed to the "breaking forward" of the imbrication consequent on the "megasplay fault".  The intpretation is according to standard Plate Tectonics:-  overthrusting is from the continental side due to colliding plates and subduction (explanation in text below and in parent article); Coloured image courtesy of  Jackson school of geosciences (http://www.jsg.utexas.edu/news/rels/111507.html).    The critical area of difference is the zone with the red arrows in (b) underneath the words "Breaking backwards".

The Nankai trough off the coast of Japan is described in the literature as a classic example of subduction controlled deformation according to Plate Tectonics.  However It is asserted here to be nothing of the sort, but rather a classic example of the deformation to be expected of Earth expansion.  In the illustration above it is asserted that the slumping interpretation of the primary seismic data (Fig.1a)  is correct, and that the Plate Tectonic interpretation, Fig.1b, is wrong.  The primary seismic data in fact highlights slumping, yet there is no mention of this in the article from which Fig.1b is reproduced.  It seems that the reason why it is ignored in the article is nothing, other than a need to bolster the theory of Plate Tectonics, where the controlling dynamics is plate movement from the oceanic side.  But seismically, this oceanward side is dead. It is not moving.  The reader is invited to consider the possibility that the theory of Plate Tectonics, for all its monolithic acceptance, is wrong, and that this simple example of the tectonics of the plate margin, underscores this fact.

Terminology:-  Slumping is a common feature of continental margins where recent deposits of unconsolidated sediments have built up to critical level of equilibrium and are dislodged by even the slightest change in stability.  Their existence is a recognised hazard to submarine infrastructure.   Their physiology and genesis is well understood and a genetic name, 'slumps' (due to 'slumping'), is well justified.

However, around the Pacific these 'slumps' assume a special and different significance because of their association with island arcs and the key role that these play in the literature of Plate Tectonics.  The landward-dipping seismic reflectors recognised in such melanges are then ascribed, not to slumping (which the convoluted and chaotic structures they describe would normally encourage), but to thrusting related to arc generation and subduction, and named "subduction complexes", or "accretionary arcs" both of which incidentally contravene the rules of nomenclature which frown on genetic descriptives.

The genetic origin of these structures is described as follows according to Plate Tectonics.

The oceanic plate pushes from the left in Fig.1b, encountering the continental buttress.  The buttress forces the oceanic plate downwards as a subducting slab.  The slab, which is already denser than the underlying mantle because it's cold  (the litany:- "the farther it gets from the ridge the colder/ denser it gets"..etc., etc.) is forced into the hotter regions of the mantle where it heats up and converts to its denser eclogite equivalent.  This conversion then allows the slab to sink under the force of gravity.   The slab now sinks like the Titanic, with the force of gravity pulling it down.

It is a fine conceptual pas-de-deux, is it not?  Plate Tectonics says on the one hand that the slab sinks because it is cold (the "cold subducting slab"), and on the other that it must be heated up in order to make it dense enough to sink.  ... But let's continue....

Just as the water washes over the disappearing hull of the Titanic (so to speak), the story goes that our sinking slab now generates currents in the mantle  which drags the continental lithosphere over the subducting slab.  On the landward side this current sets up a frictional drag at the base of the continental lithosphere, which pulls a piece (the "frontal arc" - as in the Western Pacific) off the continental buttress and pushes it (or pulls it depending on the point of reference) over the oceanic lithosphere, so that the detached piece overrides the mantle.  Thus are developed back-arc basins (as the continental margin is dragged (/'pulled') off the main hinterland landmass), frontal arcs (as the detached piece of continental margin is pulled over the mantle on the oceanward side), and so-called 'accretionary wedges' (as sediments are scraped off the ocean floors by the toe of the frontal arcs and plastered on to the continental buttress).

So what Plate Tectonics is saying here is that the push of the ocean floor towards the continents, and its secondary effect of pull generated by the sinking slab generate 'thrusts' from the landward side. That is, the continental lithosphere, ..just by sitting there doing nothing but minding its own business (and 'floating'), is not only forcing the oceanic plate down and thereby activating and driving the machinery of Plate Tectonics, but is also (by proxy of imposing subduction on the oceanic lithosphere), pulling itself off in great chunks, creating frontal arcs and back-arc basins and moreover creating 'thrusts' at their leading edges as the arcs are pulled over the disappearing subducting slab.

???

This is not only a contradiction in terms tantamount to absolute rubbish (as a runaway 'perpetual motion machine'), ..but one which is promoted by those with a vested interest in doing so as some sort of pinnacle of achievement. !!  A much simpler view is that proposed here, of the dual dynamics of overriding and slumping related to the curvature correction of the Earth's surface.
 

A bit 'iffy',  is it not? ...representing extension and gravitational collapse as 'overthrusting' due to colliding plates and thrusting.  Something like representing the flat-lying strata of the Himalayas as cumpled crust due to the collision of plates.   But that's the measure of consensus.  If you want to get published then you have to weasel your results somehow into the acceptance of Plate Tectonics, even if it does mean cramming a perfectly good round peg (slumping as above) into a cussedly doggone ornery square hole (of Plate Tectonics).  But that to the career scientist is a minor point compared to publication, which is what science is all about.  If you don't publish, you don't have a job.  It's that simple.  What you have to do then is learn to write on the ostensible line, but mean something entirely different in between them.   It needs practice, but it can be done.

You really have to feel quite sorry for them having to be so covert, not being able to come straight out with it and say what they think in case their bright shiny new finding gets rejected just because it doesn't mesh with what everybody else thinks.  ("We are a community of scientists"...")  The only solution to this is to adapt and not worry about appearing to be a dill by suggesting silly things.  Such as, just by sitting there the (floating) continental lithosphere has the power inherent within it wherever it meets an oceanic plate to rip great chunks of itself off from underneath, and shunt them over marginal sedimentary accumulations and oceanic lithosphere.

Appearing to be a dill is not important.  It's necessary after all if you want to publish and everyone in the business of publication does it anyway.  Reviewers accept this as lip service to a stupid system in which they are complicit.  The important thing is the publication and whatever will allow that to happen.   And with that publication in place (with its central theme of slumps covertly ensconced between blousy old-hat consensus, trumpeting baggage about colliding plates and boundaries and megasplays and megathrusts, and accretionary prism decollements and so on) the next publication can be planned. It's  another  classic of how to weasel potentially controversial material into consensus. First, you introduce it with throwaway significance only, ..or even disown it as rubbish, ...stating as much.  Ostensibly this is to protect the innocent, but really the intention is to put fires out in case somebody else happens to think of it before follow-up, in which case you get the opportunity to rubbish it again (another publication, ..truly a win-win situation).  Secondly, with that in place it can then be used as a central plank for following write-up.  Nor does it matter if this contradicts an earlier expose, firstly (again) since rightness or wrongness is not the point, and secondly because it can always be represented as 'new findings'.

Hat-magic, ...truly.

SLUMPING
(No plate movement)

Fig.3.  Large-scale slumping off the coast of Japan.  Plate Tectonics represents it as evidence for subduction of a seamount.    <http://www.mext.go.jp/english/news/2000/07/h000701.htm>

 

However it's a moot point is it not? ...Thrusts are thrusts, whether they are generated by the piling up of slumps, or due to the so-called collision of plates.  The real question is which is more likely from what we see, ...adjustment to vertical tectonism on an enlarging substrate as in Earth Expansion? ...or adjustment to the crumpling and collision inherent in horizontal tectonicsm as in Plate Tectonics.   The answer is to be found from the regional and global picture, than it is from any seismic section.   But it looks a rather good-looking slump to me.  Hardly a product of compression, surely.  What does it look like to you?

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