Crustal-scale boudinage and the geosyncline
( Blog for website at http://users.indigo.net.au/don/ )
Today we're doing meme-ology (again), .. and today's mnemonical meme (doubling as both a mnemonic and a meme) describes the active interfaces of crustal-scale boudinage structure as 'VIP'.
'Very Important Principle? Certainly, .. but the 'V' is for vertical and the 'P', stuttered as 'PP', is for parallel and paired. Then once the 'i' is duly noted it can be replaced with an 'a' for 'asymmetrical'.
VIP and VAP: vertically parallel-paired, and asymmetrical. And Important. Why important? Because the parallel pairing of the interfaces of the neck obviates all that was problematical about the geosyncline before it was deemed obsolete and became reinvented as the Wilson Cycle.
By solving the problem with a VIP and a VAP there is no need for any W.C. Nor anything else of Plate Tectonics. VIP and VAP means a whole new game, and had that been realised at the time of the geosyncline, Plate Tectonics would never have got up.
The problem about the geosyncline that caused it to be flushed down the W.C was, "How did anomalously thick welts of sediments deposited in depressions of the crust thousands of kilometres long come to be uplifted as chains of mountains? By what dynamic could crustal extension (/subsidence) be followed by crustal compression (/uplift) in the same location, in a belt that extended for thousands of kilometres? What was happening peripherally? Surely extension in one location would be balanced by compression building mountain belts in another elsewhere? - not in the same place. .. And vice versa when it came to inverting the welt as a mountain belt. Surely mountain building must be balanced by crustal extension and basin formation elsewhere as well?" Where were the corresponding mountain belts and basins?
The answer was, nowhere. Nowhere was there any evidence of corresponding belts that might pair with such 'accordion-like' behaviour. And so it became derisively known by some as "accordion tectonics" - a parody of reality that seems to have escaped the recent crop of inductees into the Plate Tectonic Hall of Fame - which googling "accordion tectonics" (with quotations for 1,300 entries today) will show is still alive and well. And in any case, surely buckling should happen where crust was thinner, not thicker. But the opposite was true, .. it was not only that the thick welt was buckled, but the thin crust was not!. To rebrand the situation as due to a 'Wilson Cycle' did nothing other than change the language to re-state the conundrum in the context of emerging theory of 'moving plates and subducting slabs, when doing so provided no additional understanding whatsoever but merely legitimised the conundrum while at the same time adding to its perplexity.
However by interpreting the geosyncline as crustal-scale boudinage, the problem evaporates, .. as does every other conundrum of Plate Tectonics - as well as all the luggage of language (lol) that has accumulated to describe it.
Fig.2. Geosynclinal development as crustal-scale boudinage: problem solved. Crustal inversion, ..or, what goes down, comes back up - in the same place. 1 = crust/mantle interface, 2 = asthenospheric rise. E = crust/mantle (lithosphere/asthenosphere) equilibrium. Gravity determines temporal (down first / up second), and spatial (see here) asymmetry of dynamics as the ductility contrasts of the shell-interfaces of the crust are exploited.
Recognising necklines of boudinage structure on a scale that incorporates the whole crust and (if the lithosphere is included) is certainly cognitively challenging, particularly when the upper part of the neckline is laterally displaced from the lower one, but that is precisely what is happening in the case of mantle breakthrough that has formed the ocean floors. Or at least (since scale *is* an issue) it is a useful analogy by which to understand the vertical relationship between the crust and mantle when the mantle does break through.
Surficial distension initiating the Pacific was profound. Driving above its equilibrium position, mantle lift caused a circular elevation in the Indonesian region, perhaps much like occurs as Noctis Labyrinthus on Mars. A breakout around the periphery of the dome (due to collapse and crustal loading ) then split the mantle initiating the Pacific spreading ridge. Crustal collapse, manifest as the Javanese arc and overriding of the Western Pacific margin, continued to encroach on the trailing edge of mantle growth as the ridge dilated.
Fig.2. Rise of the lower mantle initiates a circular breakout in the Indonesian region. (a) Breakthrough of the lower mantle rise (red) is accompanied by crustal collapse (grey). (b) Swivel opening of the crust during collapse duplicates (and triplicates) the Pangaean equatorial zone. Green = upper mantle. (See also)
Hemispherical torque of the Pangaean crust swivelled it open in a triplicate fan-like dilation on the Asian side to form the back-arc basins of the Western Pacific. A simpler duplicate dilation spread the American Cordilleras. A mirror of this Cordilleran duplication, less dilated but with triplicate apophyses in the region of the '-istans' ('Uzbekistan' etc), extends from the Western Pacific through the Tarim Basin to the Mediterranean (previous link).
The breakout appears to have had a very close analagous comparison with that relating Noctis Labyrinthus to Valles Marineris on Mars, and it is most intriguing to consider, given the evidence for the massive extrusion of water apparently related to these structures, if something similar might have accompanied the birth of the oceans on Earth during the Mesozoic (and if a fate similar to the dessication on Mars may await Earth as Pacific extrusion dissipates). It is quite possible that the initial breakout was water, to be followed by magmatic extrusion (it being well known that water forms the largest proportion of gaseous magmatic exrtrusion).
Hawaii may illustrate a further comparison, because continental reconstruction shows it appearing to have been closely central to this initial doming on the Pangaean Earth, a comparison supported by its deeper 'hotspot' status, and its almost daily seismicity.
?? [ Noctis Labyrinthus / Valles Marineris / Water / Olumpus Mons on Mars == Indonesian bubble / Pangaean equatorial dilation / Water(?) / Hawaiian Chain on Earth ] ??( .. Just saying.. )
Further displacement of the spreading ridge from the Indonesian bubble (crustal dome) occurred by a combination of crust-uppermantle detachment, detachment within the upper mantle itself (such as is apparent in the Indian Ocean), and growth at the spreading ridge.
Compared to this forceful breakout with its swivelling crustal dilations, the Atlantic appears to have been a relatively innocuous, passive affair, where the mantle has broken through the crust only to the extent of rising to its equilibrium position to fill the gap created by crustal rupture as it trailed Pacific dilation. Unhinging of the Caribbean pivot of American dilation contemporaneous with Atlantic opening represents stretching around the periphery of the Pacific (Fig.1 here).
The difference between active and passive mantle behaviour is dependent on many things, .. rates of extension, crustal stiffness /viscosity, asymmetries of developing structure, but most of all it is dependent on what caused the massive circularity of mantle breakout in the Indonesian region in the first place, an answer to which must be found in a very rapid (geologically speaking) asymmetrical disturbance of the Earth's gravitational field and its rotation, .. which is still happening.
Moonpull due to capture causing a shift in the Earth's gravitational centre? What else could cause a spherical disturbance of the Earth's gravitationally-formed spherical shells? (The gravitational beat of once-a-day Earth rotation meets the drum of a once-a-month Moon?)
Geology began with observations of stratigraphic sequence, fossils, and questions of geological time and igneous intrusion - granitoids from the base of the crust and basalt from the mantle rising in advance of the mantle itself, .. observations that were further superimposed by structural disturbance, and all smoothed by erosion wherever the crust was raised above sea-level. Its simplicity is a bit overblown now as evermore geologists (and modelling geophysicists) have obscured it, but it is still recognisable as a consequence of crustal-scale boudinage. The analogy does break down somewhat when we say, "boudinage of the lithosphere', because as modification of Pangaean crust it's not really very clear exactly what the substance of the lithosphere, or its areal distribution actually is when we step aside from its present-day definitive earthquake expression. But in a nutshell boudinage of the crust (i.e., wholesale extension of the crust) (i.e., global expansion) and its myriad geological effects steered by gravity and Earth rotation, does provide a very useful analogue (model) by which to understand the evolution of the Earth's outer, more brittle shell. However questions do arise in regard to the massive increase in the volume of the mantle that has happened, and the relationship of both to Earth's spin, the magnetic field and questions re the creation of matter and increase in mass - and what mass actually is in a context of the quantum world of its existence.
The reason the importance of this essential geo-simplicity is not more widely recognised (and why geology has become mired in the complexity of platespeak) lies in the contrast between the anatomical ('elemental') approach required by reductive science. and the much more wholistic approach required to identify patterns of structure at the larger scale, a contrast that is nicely written in the history of the subject because from the earliest days the principle of scale invariance (the maxim that the small-scale structures are the key to the larger scale) has been widely applied to structure such as joints, faults and folds, .. but curiously not to boudinage.
"..Relatively little attention has been given to geological structures that form when layered sequences, or rocks with a fabric are compressed at a high angle to, and/or extended in the plane of the layering or fabric. The reason for this is not clear, for 'extension' structures are much more common in nature than one would infer from the paucity of literature concerning them." (Price and Cosgrove, 1990. Analysis of Geological Structures, p.405. Cambridge University Press,. 502pp; introductory paragraph to the chapter on boudinage)
The reason why it hasn't is because the cognitive challenge of recognising pattern is not met by the reductive nature of 'science', and goes to the heart of the difference between the linearity of the reductive scientific mind that likes to pull things apart to see how they work, and the more wholistically engaged, inductive approach that prefers to see things in terms of the contextual framework of the larger scale - "the whole as more than the sum of its parts". Even though there has been tacit recognition since the term was coined that "boudinage occurs on all scales" it is only today that there is some interest in exploring the implications of this, even though this typically refers to highly simplistic two-dimensional sectional representations of the crust in a context of Plate Tectonics. Its application to the larger three-dimensional extent of the Earth's surface still largely remains to be explored.
The failure to properly appreciate the connection between basin formation and its deformation embodied in the concept of the geosyncline mentioned above was the brick wall encountered when geologists failed to meet the challenge of their own maxim of scale invariance as it applied to boudinage. Why did they fail to meet the challenge? Because the quirky etymology of 'sausages' got lost in translation between outcrop and crustal scales, and because the active process of boudinage is not really one of forming boudins at all, but of forming the necks that separate them; boudins are only the passive result of actively developing necks, and whilst two necks are needed to define a boudin, one neck will do to define the process: one neck does not a boudin make, but the process of boudinage occurs nevertheless.
Geologists know all about big boudinage of course, but just tend to see it in terms of one-to-one equivalence with its small-scale counterpart. The implications of process in time and space just hasn't quite penetrated their collective consciousness in a way that will help them (as a collective) to challenge Plate Tectonics. If it had there would have been no dismissal of the geosyncline and no adoption of the Wilson cycle.
They need a meme to help them conceptualise and vocalise. United they stand, but as sheeples they don't.
And so, .. what? Do we wait for one to memenate from our stellar institutions of learning that will help transport the VIP (very important principle) of vertical parallel pairing of crustal-scale boudinage to the forefront of geological lobotomemes. I don't think so. So, .. in the memetime, ...
"Meme us up, Scotty." :-))
[OK - because Plate Tectonics evidently can't.]
(Vertical, parallel-paired, asymmetrical - and by no memes off the planet.)
[ See also - Debunking Plate Tectonics - at :-