Just musing (I don't know if I would call it thinking).. ...that there seems to be a curious glitch in the THINKING of PTers which intriugues me. (I hope they haven't been 'just musing' too all this time) I'd be interested in others' comments.
Structural geology of the last century has been historically involved with stresses arising "in the plane of the Earth's crust", a notion which has carried over (in the 50's and sixties - before any Yuri Gagarin, i.e., space exploration) to the idea of PLATE TECTONICS. It cements the idea of things moving about on a flat surface creating sideways stresses, and reactions to them ("..In the plane of..", ...plates..., and flat maps to illustrate all this, sort of all go together - nicely.) The question is, how much has this two dimensional 'flatness' of planes and plates been an impediment to thinking (thinking)?
I mean, everyone knows that the Earth is not flat, and that flat maps are a convenience of printing presses, and that at the scale of global inquiry the Earth is in fact a round rotating sphere, with body stresses arising from gravitational (i.e.vertical) instabilities related to its rotation and position re. the Sun and the Moon. Plate tectonics even has this idea of CONVECTION CURRENTS - huge transports of 'up' and (by inference at least) 'down'. Yet when it comes to affecting the crust, it wants to translate this huge potential energy source for immediate local deformation into a sideways force thousands of kilometres away... It even recognises the potential for direct gravitational collapse off ridges but realises this through a *thermal* correction as 'ridge push', ...but this too just as an assistant to 'slab-pull'. The two go nicely (sideways) together. It's a bit longer to say "'ridge-push' - 'slab-pull' " (and an absolute bugger to type), rather than 'conveyor belt', but the import is the same.
The point is, we have all of this huge store of potential energy for tectonic force (offered to us on a plate), called ridges, and Plate tectonics wants to transmute it into horizontalness, and has gone to considerable jiggery-pokery lengths to do it. If the primary forces are 'up' (and OK down too if you like), surely horizontality is simply just second order (gravitational) correction?
So the question is, why does plate tectonics want to focus on the second order 'spinoff' effect ('plate' / 'flat') and not on the primary 'up' cause? It even disregards the 'up-to-half-a-metre-a-day' vertical tidal flux as 'noise', in favour of the centimetre a year sideways.
I've got a feeling that if plate tectonicists cottoned on to the idea that the earth is round and rotating, that plate tectonics wouldn't exist, because all this 'sideways-ness' is really a hangover from the flatness of pre-Yuri Gagarin days. Seems to me anyhow. I mean....we have all this 'uplift and erosion', why isn't *this the *primary thing, instead of it being somehow the result of 'sideways-is-King'? (Who is this King anyhow? Has he published anything? Does he at least wear a crown?)
Any ideas why this fixation on sideways instead of vertical, when the primary dynamics are vertical? (...'tablecloths [on a table) and vices (on a bench) ... a few of my favourite things perhaps? Some sort of fetish? Drunken pub lunches on field trips?? When I muse thereupon, these are the only images I get about sideways as a *primary force, because geologically speaking I don't see that much evidence for it.
Right, just musing. God help us all if you ever thought.
> Any ideas why this fixation on sideways instead of vertical, when the > primary dynamics are vertical? (...'tablecloths [on a table) and > vices (on a bench) ... a few of my favourite things perhaps? Some > sort of fetish? Drunken pub lunches on field trips?? When I muse > thereupon, these are the only images I get about sideways as a > *primary force, because geologically speaking I don't see that much > evidence for it.
> How about you?
For the same reason we don't feel the stresses of spinning 24,000 miles in the course of 24 hours. This is the equivalent of a child asking "Why don't I spin off the Earth if it spinning so fast?"
don findlay wrote: > Structural geology of the last century has been historically involved > with stresses arising "in the plane of the Earth's crust", a notion > which has carried over (in the 50's and sixties - before any Yuri > Gagarin, i.e., space exploration) to the idea of PLATE TECTONICS. It > cements the idea of things moving about on a flat surface creating > sideways stresses, and reactions to them ("..In the plane of..", > ...plates..., and flat maps to illustrate all this, sort of all go > together - nicely.) The question is, how much has this two > dimensional 'flatness' of planes and plates been an impediment to > thinking (thinking)?
Your point is important, but in my opinion, the PTers quite successfully explained the reason of the bending island arcs surrounding the Pacific Ocean - it's exactly because tilting plates on a sphere require tilted edges. The Himalayas are bent in the same way for the same reason. In many other instances, the Earth's shape is not mentioned explicitly just because the area considered is to small for the Earth's shape to be relevant.
> I mean, everyone knows that the Earth is not flat, and that flat maps > are a convenience of printing presses, and that at the scale of global > inquiry the Earth is in fact a round rotating sphere, with body > stresses arising from gravitational (i.e.vertical) instabilities > related to its rotation and position re. the Sun and the Moon. Plate > tectonics even has this idea of CONVECTION CURRENTS - huge transports > of 'up' and (by inference at least) 'down'. Yet when it comes to > affecting the crust, it wants to translate this huge potential energy > source for immediate local deformation into a sideways force thousands > of kilometres away...
Due to the Earth's gravitation, the up and down movements *have* to stop at the surface. Did you ever watch a pot of boiling water? There are lots of convection currents, but the surface is almost smooth. The convection currents produce horizontal currents at the surface and any paricles lighter than water (e.g. tea) gather at places where the currents meet and start their downward motion. Do that test and watch it carefully - you'll find several matches to tectonics.
> The point is, we have all of this huge store of potential energy for > tectonic force (offered to us on a plate), called ridges, and Plate > tectonics wants to transmute it into horizontalness, and has gone to > considerable jiggery-pokery lengths to do it. If the primary forces > are 'up' (and OK down too if you like), surely horizontality is simply > just second order (gravitational) correction?
The horizontal vertical movements go together - one is impossible without the other. No first or second order.
> So the question is, why does plate tectonics want to focus on the > second order 'spinoff' effect ('plate' / 'flat') and not on the > primary 'up' cause? It even disregards the > 'up-to-half-a-metre-a-day' vertical tidal flux as 'noise', in favour > of the centimetre a year sideways.
The vertical tidal movement adds up to zero over a 12 h period. The horizontal tectonic movement accumulates to 1000s of km.
There are several instances where you can see the results of the vertical movement at the surface: Iceland, Arabia, East Africa are at higher elevations than they should be, just because mantle material is pushing from below (another reason is that the crust below is warmer and lighter). We are talking about many hundreds or even few thousand meters elevation - is that nothing?
Cheers, Christof -- Christof Kuhn Inst. f. Angewandte Geologie, Univ. f. BoKu Wien, Austria
Christof Kuhn <Christof.K...@boku.ac.at> wrote in message <news:3e6e2674$0$13160$3b214f66@news.univie.ac.at>... > don findlay wrote: > > Structural geology of the last century has been historically involved > > with stresses arising "in the plane of the Earth's crust", a notion > > which has carried over (in the 50's and sixties - before any Yuri > > Gagarin, i.e., space exploration) to the idea of PLATE TECTONICS. It > > cements the idea of things moving about on a flat surface creating > > sideways stresses, and reactions to them ("..In the plane of..", > > ...plates..., and flat maps to illustrate all this, sort of all go > > together - nicely.) The question is, how much has this two > > dimensional 'flatness' of planes and plates been an impediment to > > thinking (thinking)?
> Your point is important, but in my opinion, the PTers quite successfully > explained the reason of the bending island arcs surrounding the Pacific > Ocean - it's exactly because tilting plates on a sphere require tilted > edges. The Himalayas are bent in the same way for the same reason. In > many other instances, the Earth's shape is not mentioned explicitly just > because the area considered is to small for the Earth's shape to be > relevant.
> > I mean, everyone knows that the Earth is not flat, and that flat maps > > are a convenience of printing presses, and that at the scale of global > > inquiry the Earth is in fact a round rotating sphere, with body > > stresses arising from gravitational (i.e.vertical) instabilities > > related to its rotation and position re. the Sun and the Moon. Plate > > tectonics even has this idea of CONVECTION CURRENTS - huge transports > > of 'up' and (by inference at least) 'down'. Yet when it comes to > > affecting the crust, it wants to translate this huge potential energy > > source for immediate local deformation into a sideways force thousands > > of kilometres away...
> Due to the Earth's gravitation, the up and down movements *have* to stop > at the surface. > Did you ever watch a pot of boiling water? There are lots of convection > currents, but the surface is almost smooth. The convection currents > produce horizontal currents at the surface and any paricles lighter than > water (e.g. tea) gather at places where the currents meet and start > their downward motion. Do that test and watch it carefully - you'll find > several matches to tectonics.
> > The point is, we have all of this huge store of potential energy for > > tectonic force (offered to us on a plate), called ridges, and Plate > > tectonics wants to transmute it into horizontalness, and has gone to > > considerable jiggery-pokery lengths to do it. If the primary forces > > are 'up' (and OK down too if you like), surely horizontality is simply > > just second order (gravitational) correction?
> The horizontal vertical movements go together - one is impossible > without the other. No first or second order.
> > So the question is, why does plate tectonics want to focus on the > > second order 'spinoff' effect ('plate' / 'flat') and not on the > > primary 'up' cause? It even disregards the > > 'up-to-half-a-metre-a-day' vertical tidal flux as 'noise', in favour > > of the centimetre a year sideways.
> The vertical tidal movement adds up to zero over a 12 h period. The > horizontal tectonic movement accumulates to 1000s of km.
> There are several instances where you can see the results of the > vertical movement at the surface: Iceland, Arabia, East Africa are at > higher elevations than they should be, just because mantle material is > pushing from below (another reason is that the crust below is warmer and > lighter). We are talking about many hundreds or even few thousand meters > elevation - is that nothing?
> Cheers, Christof
Talking about island arcs; have you noticed how similar the north of the Pacific and Indian oceans are? How the outlines of seas seem to form a circle on a globe? How the outline of Africa so resmbles that of the Pacific? How the east coast of north America so resembles that of the east coast of Asia that an early explorer might easily mistake them?
Or am I being silly?
In for a penny then:
Has anyone noticed how similar weather patterns are in regions where the coastlines look similar? For example look at the coastline of the Med. from Spain to Italy and compare the regional penchant for low pressure (to bring what we Brits call good weather) to that of areas that look similar. Areas like the north of the Indian and Pacific oceans mentioned above.
> Right, just musing. God help us all if you ever thought.
> > Any ideas why this fixation on sideways instead of vertical, when the > > primary dynamics are vertical? (...'tablecloths [on a table) and > > vices (on a bench) ... a few of my favourite things perhaps? Some > > sort of fetish? Drunken pub lunches on field trips?? When I muse > > thereupon, these are the only images I get about sideways as a > > *primary force, because geologically speaking I don't see that much > > evidence for it.
> > How about you?
> For the same reason we don't feel the stresses of spinning 24,000 > miles in the course of 24 hours. This is the equivalent of a child > asking "Why don't I spin off the Earth if it spinning so fast?"
> Andy
Don't you? I find the stress of it all just too, too much, and gotta crash every night. And don't worry about spinning off the Earth if you'd rather be sucked down one of them subduction zones.
This plate tectonics, it has that curious 'in-and-outness', ..flitting in and out of reality... about it. It all hangs together in a curious sort of way, and yet there's a warpedness about it that is quite difficult to describe - like one of those weird distorting mirrors. (scary tectonics). What's even more weird and scary is that so many people go along with it, and even like it, ..reckon it's the bees knees (democracy in action).
Of course, it's not that that's scary at all, because I'm sure everyone can think of something wrong with it, that doesn't gel with them, that doesn't ring true, sound right, the full ten cents - even the most ardent Ptero. What is scary is that they prefer to ignore these small, querulous voices that hint at lies, and instead go along with it all. The stuff of totalitarianism is alive and well apparently, and not confined by any means to politics (of the darker sort, of course)
In the interest of exorcism, cleansing the devil of pteromancy from the children of mankind -or if you prefer, a worm tablet- (and getting rubbished for it 'coz I refuse to acknowledge the connection between hot air balloons, soup, and the creation of ocean floors).... don @ <http://users.indigo.net.au/don/ee/p1-page1.html> (...Feed me, O thou Great Jehova...)
Christof Kuhn <Christof.K...@boku.ac.at> wrote in message <news:3e6e2674$0$13160$3b214f66@news.univie.ac.at>... > don findlay wrote: > > Structural geology of the last century has been historically involved > > with stresses arising "in the plane of the Earth's crust", a notion > > which has carried over (in the 50's and sixties - before any Yuri > > Gagarin, i.e., space exploration) to the idea of PLATE TECTONICS. It > > cements the idea of things moving about on a flat surface creating > > sideways stresses, and reactions to them ("..In the plane of..", > > ...plates..., and flat maps to illustrate all this, sort of all go > > together - nicely.) The question is, how much has this two > > dimensional 'flatness' of planes and plates been an impediment to > > thinking (thinking)?
> Your point is important, but in my opinion, the PTers quite successfully > explained the reason of the bending island arcs surrounding the Pacific > Ocean - it's exactly because tilting plates on a sphere require tilted > edges. The Himalayas are bent in the same way for the same reason. In > many other instances, the Earth's shape is not mentioned explicitly just > because the area considered is to small for the Earth's shape to be > relevant.
Right, ..I'd forgotten about the ' principle of intercepts'. This is what I mean by distorting mirrors. The POINT:- the Earth is round because gravity rules - it will adjust even half a meter of distortion to zero in a matter of hours (apparently) - and yet Pteros want this curved plate at ridges to flatten off as it migrates across the oceans to arrive at the subduction zone (after millions of years), flat as a tack. Why, it might even curve upwards (since it loses its heat upwards). That would accentuate the curvature. Or would it curve downwards as the mantle cools and shrinks (hmm, ... but then the arcs would curve the other (wrong) way). So which? Does the plate curve *down as the mantle shrinks? Is it *flat? Or should it curve *up as it loses its heat to the oceans? I would imagine (given that gravity rules) it would stay curved exactly as it was at the ridges. But it should be easy to tell if we look at the ocean floor, ...and I don't think it flattens off at all. But Pteros (looking in the mirror of their model) might see things differently.
But say it's flat. Then what? Does it tilt (to give the curvature required)? ...or does it 'scrunch' (against irregularities in the brittle crust - and so takes on the irregularities of the continental crust. Or does it just, ...well, ..sink - because its 'time' has come (rate of loss of heat). Plate tectonics invokes all three depending on requirements, like three overprinted reflecting morphs. It even invokes a fourth - tangential overshoot (to give us ophiolites), but thankfully not much (which is why there are not many). (Wierd reflecting mirrors - a Lady for All Seasons, turn, turn..)
So, is the principle of intercept really all that credible? (As far as explaining the bend in the Himalayas is concerned, I think there are other parameters involved (just posted <http://users.indigo.net.au.don/ee/indocean.html> (Fig.1)
> > I mean, everyone knows that the Earth is not flat, and that flat maps > > are a convenience of printing presses, and that at the scale of global > > inquiry the Earth is in fact a round rotating sphere, with body > > stresses arising from gravitational (i.e.vertical) instabilities > > related to its rotation and position re. the Sun and the Moon. Plate > > tectonics even has this idea of CONVECTION CURRENTS - huge transports > > of 'up' and (by inference at least) 'down'. Yet when it comes to > > affecting the crust, it wants to translate this huge potential energy > > source for immediate local deformation into a sideways force thousands > > of kilometres away...
> Due to the Earth's gravitation, the up and down movements *have* to stop > at the surface. > Did you ever watch a pot of boiling water? There are lots of convection > currents, but the surface is almost smooth. The convection currents > produce horizontal currents at the surface and any paricles lighter than > water (e.g. tea) gather at places where the currents meet and start > their downward motion. Do that test and watch it carefully - you'll find > several matches to tectonics.
Ah, the pot of tea again (variation on the pot of soup). You know Christof that Pteros don't like the one about tea for exactly the reason you say - that the surface stays so resolutely and damnably inert (!) That surface does remain very smooth despite roiling convection directly below. The 'skin' has to break before a piece will be carried along. The force (surface tension) holding the surface together has to be overcome. And I see no analogue of surface tension in plate tectonic models, which are exclusively about Raleigh numbers (ratios of heat below to heat above) and Taylor numbers (something to do with whether you get laminar or chaotic flow around driving cylinders (if there are any), which are this or that far apart and rotating at different speeds). Cylinders where (if the flow itself is supposed to be the cylindrical bit)? And three- dimensionally curved ones of course (how do they fit? What are they made of?).
As far as the broken tea bag goes, it all depends on whether the tea leaves are caught in the 'skin' , which, when you stir the pot, slows down and stops very quickly (if the water's a bit hard), and the tea leaves fall down the slope to the centre long before the vigourous mantle slows down, ...or whethere they stay in the mantle and keep going round and around and up and down despite the immobility up top. If the analogy is to be used (and that skin is really something) then surface tension *has to be taken into account. All I've ever seen skin do, is pull apart. I've never seen broken edges wrinkle up (have I?), and I suppose that's because skin is pretty strong, relative to the forces imparted (at that scale) by the frictional drag of convective flow. (tensional effects requiring much less force than compressional effects)
> > The point is, we have all of this huge store of potential energy for > > tectonic force (offered to us on a plate), called ridges, and Plate > > tectonics wants to transmute it into horizontalness, and has gone to > > considerable jiggery-pokery lengths to do it. If the primary forces > > are 'up' (and OK down too if you like), surely horizontality is simply > > just second order (gravitational) correction?
> The horizontal vertical movements go together - one is impossible > without the other. No first or second order.
Ooohh.. As usual, this is exactly what plate tectonics says when explaining the theory, but it's not what it says when referring the theory to the field evidence - in fact it gets itself into a bit of a knot right away, about first and second order, by not even being clear whether the ridges are being *pushed apart (by the intruding magma - and later by gravitational correction - "ridge-push") or whether the ridges are being *pulled apart by gravitational collapse off the ridges (and the partial melt magma is just so much passive space-filling)("ridge-pull"?. What's driving this shemozzle? ( Shades of the morphing mirror again.) Driver? Only the ridges *keep(*keep) driving/ being driven* above their thermal and gravitational equilibrium - i.e. apparently ever faster for the last 200my. And since all the radiogenic heat has mostly been lost long ago, this means plate tectonics has to explain (in view of the geological record) what amounts to really a very substantial excess of heat over its original budget (even forgetting about how it manages to get it all lined up to produce 'convection cells' (that break regularly along their length) - and keep them there).
If people want to scale it up to make it into mantle overturn, and make analogies with pots of tea and plates of soup, then they have to scale up surface tension as well, to take account of how convection interacts with a surface (both continental and oceanic). I don't see any mention of surface tension analogues in plate tectonics. And anyhow, If I'm weightless at the centre of Earth, presumably a subducting slab would be too, if it managed to get that far. So just how far does it manage to sink before this 'weightlessness' (and lack of 'slab-pull') becomes a real problem for convection? I bet Pteros would say either it dissolves before it gets there, ...soaks up heat as it does so, and so accelerates the convection process (perpetual motion machine...) ..or, being weightless, is carried along by laminar flow (Look Ma! No pull!) Or both, being the imaginative folks they are.
Convection is an assumption, and to my way of thinking a daft one. Really, an admission by plate tectonics that it doesn't really have an answer to what's going on, and a constructive approach to start "dealing honestly at the data" would be an infinite improvement on what we've got - highlighting some of the falsifiers. It's this refusal that's a bit 'scary' (scary tectonics). If they can get away with this sort of thing in science, we can hardly complaina about politicians whose job it is to pull the wool over our eyes.
> > So the question is, why does plate tectonics want to focus on the > > second order 'spinoff' effect ('plate' / 'flat') and not on the > > primary 'up' cause? It even disregards the > > 'up-to-half-a-metre-a-day' vertical tidal flux as 'noise', in favour > > of the centimetre a year sideways.
> The vertical tidal movement adds up to zero over a 12 h period. The > horizontal tectonic movement accumulates to 1000s of km.
> There are several instances where you can see the results of the > vertical movement at the surface: Iceland, Arabia, East Africa are at > higher elevations than they should be, just because mantle material is > pushing from below (another reason
Weatherlaw...@hotmail.com (Michael McNeil) wrote in message <news:290b5eaf.0303111615.46f5a637@posting.google.com>... > Talking about island arcs; have you noticed how similar the north of > the Pacific and Indian oceans are? How the outlines of seas seem to > form a circle on a globe? How the outline of Africa so resmbles that > of the Pacific? How the east coast of north America so resembles that > of the east coast of Asia that an early explorer might easily mistake > them?
You haven't been paying attention in class mate. You'll need to come down and sit with Big-fella.
> Has anyone noticed how similar weather patterns are in regions where > the coastlines look similar? For example look at the coastline of the > Med. from Spain to Italy and compare the regional penchant for low > pressure (to bring what we Brits call good weather) to that of areas > that look similar. Areas like the north of the Indian and Pacific > oceans mentioned above.
Neil, there are few really with the incisive perspicacity such as yourself. Redeem yourself and you can go back to your seat. ...This was the question I asked you before - whether you thought from a legal point of view the crust regulates the weather, or the weather regulates the crust, but you had something else on your mind - fishfingers or something. http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&safe=off&selm=5f16... Polarity of cause and effect, and the inclusion of the 'missing link' is ever the problem when we look at things bigger'n us. http://users.indigo.net.au/don/ee/p2-page2.html#steel Don.
Ok - many pters will say, I'm wasting bandwidth (you are not the first earth expansionist to deal with fruitlessly here), but here we go.
don findlay wrote:
> Right, ..I'd forgotten about the ' principle of intercepts'. This is > what I mean by distorting mirrors. The POINT:- the Earth is round > because gravity rules - it will adjust even half a meter of distortion > to zero in a matter of hours (apparently) - and yet Pteros want this > curved plate at ridges to flatten off as it migrates across the oceans > to arrive at the subduction zone (after millions of years), flat as a > tack.
Who says that??? Crust is spherical and remains spherical until it is deformed at a destructive margin. No need for flatting off. Don't know what you speak of.
> Why, it might even curve upwards (since it loses its heat > upwards). That would accentuate the curvature. Or would it curve > downwards as the mantle cools and shrinks (hmm, ... but then the arcs > would curve the other (wrong) way). So which? Does the plate curve > *down as the mantle shrinks? Is it *flat? Or should it curve *up as it > loses its heat to the oceans? I would imagine (given that gravity > rules) it would stay curved exactly as it was at the ridges. But it > should be easy to tell if we look at the ocean floor, ...and I don't > think it flattens off at all. But Pteros (looking in the mirror of > their model) might see things differently.
I'm afraid I cannot follow your thoughts. Why should crust bend upwards? Crust maintains the same shape until it is pushed below another plate. Spherical geometry requires a convex boundary (viewed from the subducted plate). The deformation due to shrinking by cooling is so little that it has no visible geometric effect (if the radius of the surface decreases by 1km over 2000km, that's not really significant, you'll have to admit).
> But say it's flat. Then what? Does it tilt (to give the curvature > required)? ...or does it 'scrunch' (against irregularities in the > brittle crust - and so takes on the irregularities of the continental > crust. Or does it just, ...well, ..sink - because its 'time' has come > (rate of loss of heat). Plate tectonics invokes all three depending > on requirements, like three overprinted reflecting morphs. It even > invokes a fourth - tangential overshoot (to give us ophiolites), but > thankfully not much (which is why there are not many). (Wierd > reflecting mirrors - a Lady for All Seasons, turn, turn..)
Maybe I've missed a point, but I cannot find out why you insist on pters talking about flat surfaces.
> Ah, the pot of tea again (variation on the pot of soup). You know > Christof that Pteros don't like the one about tea for exactly the > reason you say - that the surface stays so resolutely and damnably > inert (!) That surface does remain very smooth despite roiling > convection directly below. The 'skin' has to break before a piece > will be carried along. The force (surface tension) holding the > surface together has to be overcome. And I see no analogue of surface > tension in plate tectonic models, which are exclusively about Raleigh > numbers (ratios of heat below to heat above) and Taylor numbers > (something to do with whether you get laminar or chaotic flow around > driving cylinders (if there are any), which are this or that far apart > and rotating at different speeds). Cylinders where (if the flow itself > is supposed to be the cylindrical bit)? And three- dimensionally > curved ones of course (how do they fit? What are they made of?).
I don't see why the surface tension should be important for the convection in the tea pot, particularly if we're speaking about large pots.
> As far as the broken tea bag goes, it all depends on whether the tea > leaves are caught in the 'skin' , which, when you stir the pot, slows > down and stops very quickly (if the water's a bit hard), and the tea > leaves fall down the slope to the centre long before the vigourous > mantle slows down, ...or whethere they stay in the mantle and keep > going round and around and up and down despite the immobility up top. > If the analogy is to be used (and that skin is really something) then > surface tension *has to be taken into account. All I've ever seen > skin do, is pull apart. I've never seen broken edges wrinkle up (have > I?), and I suppose that's because skin is pretty strong, relative to > the forces imparted (at that scale) by the frictional drag of > convective flow. (tensional effects requiring much less force than > compressional effects)
Ok, the broken tea bag is not an ideal comparison since the tea leaf bits are denser than water if saturated (as long as they're dry, it's mostly this confusing surface tension that holds them at the surface). Let's consider a really large pot (several m diameter) and wood chips (several cms in diameter) swimming at the surface. Agree that surface tension is neglegible here? Agree that the chips gather in those places at the surface where the convection currents meet? That's the way the continents move (apart from the subduction and melting effects, of course).
> And anyhow, If I'm weightless at the centre of Earth, presumably a > subducting slab would be too, if it managed to get that far. So > just how far does it manage to sink before this 'weightlessness' (and > lack of 'slab-pull') becomes a real problem for convection? I bet > Pteros would say either it dissolves before it gets there, ...soaks up > heat as it does so, and so accelerates the convection process > (perpetual motion machine...) ..or, being weightless, is carried along > by laminar flow (Look Ma! No pull!) Or both, being the imaginative > folks they are.
If you would have done a bit of reading, you would have found out that oceanic crust makes it few hundreds of km below the surface, where gravitation is more than 90% of that at the surface. Nobody's talking about the crust moving to the earth center.
> Convection is an assumption, and to my way of thinking a daft one. > Really, an admission by plate tectonics that it doesn't really have an > answer to what's going on, and a constructive approach to start > "dealing honestly at the data" would be an infinite improvement on > what we've got - highlighting some of the falsifiers. It's this > refusal that's a bit 'scary' (scary tectonics). If they can get away > with this sort of thing in science, we can hardly complaina about > politicians whose job it is to pull the wool over our eyes.
Maybe you should do a bit of further reading to highlight some of the falsifiers. So far I haven't found anything in pt falsified by your arguments.
> Not at all. In fact, Earth Expansion would up the ante considerably, > and say uplift is what its *a.a..all* about. Diapir rise (the > Pacific) and gravitational collapse (the circumglobal mountain belt) - > an uplift of a few thousand *kilometres in fact, all over the place, > not paltry metres here and there.
Maybe I should do a bit of further reading about diapir rise and gravitational collapse, but so far I don't know what you're talking about.
As you mentioned field data: I live in Austria and most of Austria is huge evidence of compression tectonics (there are few basins that are a result of crust moving away in a direction perpendicular to the compression, leaving a gap behind). Little evidence for elevation-induced tectonics (only some surficial nappes that rode down a massif that was pushed up by compression).
Cheers, Christof -- Christof Kuhn Inst. f. Angewandte Geologie, Univ. f. BoKu Wien, Austria
>Subject: Re: OK - another one for the board >From: Christof Kuhn Christof.K...@boku.ac.at >Date: 3/13/03 2:00 PM Hawaiian Standard Time >Message-id: <3e711bc9$0$13160$3b214...@news.univie.ac.at>
>Ok - many pters will say, I'm wasting bandwidth (you are not the first >earth expansionist to deal with fruitlessly here), but here we go.
>don findlay wrote:
>> Right, ..I'd forgotten about the ' principle of intercepts'. This is >> what I mean by distorting mirrors. The POINT:- the Earth is round >> because gravity rules - it will adjust even half a meter of distortion >> to zero in a matter of hours (apparently) - and yet Pteros want this >> curved plate at ridges to flatten off as it migrates across the oceans >> to arrive at the subduction zone (after millions of years), flat as a >> tack.
>Who says that??? Crust is spherical and remains spherical until it is >deformed at a destructive margin. No need for flatting off. Don't know >what you speak of.
My guess is, is that he is butchering the fact that old lithosphere tends not to obey the depth age relation, it is not as far below sea-level as one might expect given its age. Some folks refer to this as the flattening of the lithosphere.
As usual, he is not communicating effectively, and you can expect to be faulted for not understanding him.
One can only imagine what happens when something like this goes through the mind of an EE'er.
Stuart Dr. Stuart A. Weinstein Ewa Beach Institute of Tectonics "To err is human, but to really foul things up requires a creationist"
Christof Kuhn <Christof.K...@boku.ac.at> wrote in message <news:3e711bc9$0$13160$3b214f66@news.univie.ac.at>... > Ok - many pters will say, I'm wasting bandwidth (you are not the first > earth expansionist to deal with fruitlessly here), but here we go.
> don findlay wrote:
> > Right, ..I'd forgotten about the ' principle of intercepts'. This is > > what I mean by distorting mirrors. The POINT:- the Earth is round > > because gravity rules - it will adjust even half a meter of distortion > > to zero in a matter of hours (apparently) - and yet Pteros want this > > curved plate at ridges to flatten off as it migrates across the oceans > > to arrive at the subduction zone (after millions of years), flat as a > > tack.
> Who says that??? Crust is spherical and remains spherical until it is > deformed at a destructive margin. No need for flatting off. Don't know > what you speak of. > Who says? I thought you did (quote):- > in my opinion, the PTers quite successfully > explained the reason of the bending island arcs surrounding the Pacific > Ocean - it's exactly because tilting plates on a sphere require tilted > edges. The Himalayas are bent in the same way for the same reason. In > many other instances, the Earth's shape is not mentioned explicitly just > because the area considered is to small for the Earth's shape to be > relevant. (unquote)
i.e. plates. The last sentence I took to mean that you were making a distinction between flat and curved. . But anyhow if you want them both curved it still doesn't explain arc shapes, unless the ocean plate is flat or curves upwards:- <http://users.indigo.net.au/don/ee/ngsub.html>
> > Why, it might even curve upwards (since it loses its heat > > upwards). That would accentuate the curvature. Or would it curve > > downwards as the mantle cools and shrinks (hmm, ... but then the arcs > > would curve the other (wrong) way). So which? Does the plate curve > > *down as the mantle shrinks? Is it *flat? Or should it curve *up as it > > loses its heat to the oceans? I would imagine (given that gravity > > rules) it would stay curved exactly as it was at the ridges. But it > > should be easy to tell if we look at the ocean floor, ...and I don't > > think it flattens off at all. But Pteros (looking in the mirror of > > their model) might see things differently.
> I'm afraid I cannot follow your thoughts. Why should crust bend upwards? > Crust maintains the same shape until it is pushed below another plate. > Spherical geometry requires a convex boundary (viewed from the subducted > plate). The deformation due to shrinking by cooling is so little that it > has no visible geometric effect (if the radius of the surface decreases > by 1km over 2000km, that's not really significant, you'll have to admit).
I would agree with you there about the "shrinking by cooling", but Plate tectonics sees it as VERY important, being responsible for the slope of the ridges, from which the ages of the ocean floors are worked out. I would see it as just gravitational adjustment on an expanding substrate. Plate tectonics calls it 'ridge-push', but sees it as thermally induced (because it wants to maintain a convective model), rather than a direct gravitational correction.
> > But say it's flat. Then what? Does it tilt (to give the curvature > > required)? ...or does it 'scrunch' (against irregularities in the > > brittle crust - and so takes on the irregularities of the continental > > crust. Or does it just, ...well, ..sink - because its 'time' has come > > (rate of loss of heat). Plate tectonics invokes all three depending > > on requirements, like three overprinted reflecting morphs. It even > > invokes a fourth - tangential overshoot (to give us ophiolites), but > > thankfully not much (which is why there are not many). (Wierd > > reflecting mirrors - a Lady for All Seasons, turn, turn..)
> Maybe I've missed a point, but I cannot find out why you insist on pters > talking about flat surfaces.
Just from how they tried to explain the shape of arcs (above link)
> > Ah, the pot of tea again (variation on the pot of soup). You know > > Christof that Pteros don't like the one about tea for exactly the > > reason you say - that the surface stays so resolutely and damnably > > inert (!) That surface does remain very smooth despite roiling > > convection directly below. The 'skin' has to break before a piece > > will be carried along. The force (surface tension) holding the > > surface together has to be overcome. And I see no analogue of surface > > tension in plate tectonic models, which are exclusively about Raleigh > > numbers (ratios of heat below to heat above) and Taylor numbers > > (something to do with whether you get laminar or chaotic flow around > > driving cylinders (if there are any), which are this or that far apart > > and rotating at different speeds). Cylinders where (if the flow itself > > is supposed to be the cylindrical bit)? And three- dimensionally > > curved ones of course (how do they fit? What are they made of?).
> I don't see why the surface tension should be important for the > convection in the tea pot, particularly if we're speaking about large pots.
But hang on, ...you brought up the tea leaf analogy to draw attention to the undisturbed surface with all that roiling convection underneath. I was just agreeing with you. Anyhow, I haven't thought much about it, but a surface tension analogy might not be a bad one. That knife edge of a subduction zone looks to me more like a big meniscus of a sort, than it does how I would expect a subduction zone to look like. How would I expect a big subduction zone to look? Something like the inverse of the ridges, i.e. a gre.ea..t lo...ong slo..o..ope down into THE CHASM,... just exactly the reverse of the great long slope up to the ridge. But we don't get it. All we get is a 'pdoing!'..or a 'bloop'. I don't see why it's not just a competency interface between the crust and the asthenosphere and/or mesosphere - with nothing 'heat-loss' about it. But I don't know (about surface tension) it would be interesting to see what a guru reckoned on how this aspect of Archimedes and buoyancy would scale up.. Surface tension has a great propensity for coagulating floaties, despite the roiling going on underneath. (Comments invited <herre> )
<more about teabags snipped>
> If you would have done a bit of reading, you would have found out that > oceanic crust makes it few hundreds of km below the surface, where > gravitation is more than 90% of that at the surface. Nobody's talking > about the crust moving to the earth center.
Yes, I know. It's the Earth's centre moving to the crust that's on the agenda. It's Pteros who want to pull all the crust back down ("where it never wanted to be") on the grounds that there's far too much heat (even still) to be accommodated. That is, even though most of the heat was lost in the beginning to give the differentiated shells - though they make a distinction between THAT heat, and the heat of radioactivity which does all the roiling and moiling. That's my question, which I don't think plate tectonics can answer. HEATLOSS#1 gives the differentiated shells (gravitational), and puts all the radioactivity where PTers want it (though it's really concentrated in the crust). HEATLOSS#2 (which is subordinate to HEATLOSS#1) roils and moils and breaks up what HEATLOSS#1 put together in the first place. Since most of the radiogenic heat (#2)has been lost long ago anyhow, the question is even more pertinent - why is radiogenic heat breaking up what gravity put together in the first place? And why, if there is still all that heat, isn't the Earth just bigger (less dense, ...and forget about the need to convect it all away inside a 'too-small' Earth?
> Maybe you should do a bit of further reading to highlight some of the > falsifiers. So far I haven't found anything in pt falsified by your > arguments.
So how then *does plate tectonics reconcile the consanguinity of transforms globally, with how it sees the segmentation of the crust into plates? How does it support its position that the plates are 'independent' of each other (any animation model) with the fact that their dynamics are clearly tied by transforms? <http://users.indigo.net.au/don/ee/zip.html>
> > Not at all. In fact, Earth Expansion would up the ante considerably, > > and say uplift is what its *a.a..all* about. Diapir rise (the > > Pacific) and gravitational collapse (the circumglobal mountain belt) - > > an uplift of a few thousand *kilometres in fact, all over the place, > > not paltry metres here and there.
> Maybe I should do a bit of further reading about diapir rise and > gravitational collapse, but so far I don't know what you're talking about.
> As you mentioned field data: I live in Austria and most of Austria is > huge evidence of compression tectonics (there are few basins that are a > result of crust moving away in a direction perpendicular to the > compression, leaving a gap behind). Little evidence for > elevation-induced tectonics (only some surficial nappes that rode down a > massif that was pushed up by compression).
> Cheers, Christof
Really, ...I thought your part of the world saw the birth of vertical tectonics, right back to the early part of the century, with 'verticalism' continued through the Middle East right into the Himalayas..... And then into the biggest uplift of all - the Pacific, the one that brought the mantle up, right down to the transition zone. The push you're talking about is just the rumpling that goes with gravitational collapse. That's all, ...nothing complicated about it.... These ridges, uplifts, go all around the world, give us a huge energy potential source for gravitational tectonics. Ridge push? No problem in the mantle sector, but Pteros don't want, or can't
...
Ok - this shall be my last post in this thread - when I look at your website, I see that we are talking from two very different points of knowledge and understanding - one of us got things screwed up, maybe it's me, but I guess it's you...
don findlay wrote:
>Who says? I thought you did (quote):- >>in my opinion, the PTers quite successfully >>explained the reason of the bending island arcs surrounding the Pacific >>Ocean - it's exactly because tilting plates on a sphere require tilted >>edges. The Himalayas are bent in the same way for the same reason. In >>many other instances, the Earth's shape is not mentioned explicitly just >>because the area considered is to small for the Earth's shape to be >>relevant. (unquote)
> i.e. plates. The last sentence I took to mean that you were making a > distinction between flat and curved.
If you consider an area 100 by 100 km, the horizontal differences created by the spherical surface of the earth are so small that they can be neglected. When we talk about larger areas, the Earth's shape *is* relevant, of course. Yet, most of the Earth's crust is bent with the same radius - independent on time and space. Only those parts are deformed that are subducted. See below.
> But anyhow if you want them > both curved it still doesn't explain arc shapes, unless the ocean > plate is flat or curves upwards:- > <http://users.indigo.net.au/don/ee/ngsub.html>
I'm afraid you've got something wrong about imagining how a convex surface (such as the Earth's crust) changes if it is pushed downwards. If you produce a hollow in a ping pong ball, it's border forms exactly a circle. If we look at a point on the border in detail, we see that the new slope of the surface dips gently towards the centre of the ball, and the neighbour points on the border have the same dip angle. If look at the border from the undeformed (yet spherical) surface, the border to the dipping area is convex (as any circle is convex if viewed from outside). A subduction arc looks exactly the same: in front of the arc, the surface is spherical, with its centre identical with the Earth's centre. A portion of a perfect ball (if we leave aside the ellipsoid feature, which is negligible for our issue).
If the surface collides with another surface, obviously something has to happen. Gravitation leaves only one solution: the denser surface dips below the lighter surface (subduction). The border between the plates has to be part of a circle as in the ping pong ball analogy. If the large-scale border between the plates are not circular, the new border consists of a chain of circular segments, with the junctions on weak spots in plate, where the subducted part is ripped into two.
Try with ping pong ball, an orange, a soccer ball, whatever you like. You'll see that there is no occurrence of planes. Of course cartographers have to use planar maps - how could you post a globe to the Internet or print it in a book?
> I would agree with you there about the "shrinking by cooling", but > Plate tectonics sees it as VERY important, being responsible for the > slope of the ridges, from which the ages of the ocean floors are > worked out. I would see it as just gravitational adjustment on an > expanding substrate. Plate tectonics calls it 'ridge-push', but sees > it as thermally induced (because it wants to maintain a convective > model), rather than a direct gravitational correction.
Of course it could be possible that the earth is expanding at the mid-ocean ridges. But I cannot see any evidence of this. As the diameter of the Earth grows, the radius of the surface does so too. Did you ever try to make an orange peel flat? The margin will be torn resulting in several lobes, so that the peel will loke like a flower in the end. Obviously, there are no gaps in the Earth's surface, neither are there active margins rectangular to the primary active margins, producing the crust required for the increasing diameter.
You write a lot about transform faults - with an expanding earth, the transform faults could not be parallel, but their distance would have to grow when you travel away from the "primary" mid-ocean ridge. I cannot find any occurrence of this feature on the Earth.
> But hang on, ...you brought up the tea leaf analogy to draw attention > to the undisturbed surface with all that roiling convection > underneath. I was just agreeing with you. Anyhow, I haven't thought > much about it, but a surface tension analogy might not be a bad one. > That knife edge of a subduction zone looks to me more like a big > meniscus of a sort, than it does how I would expect a subduction zone > to look like. How would I expect a big subduction zone to look? > Something like the inverse of the ridges, i.e. a gre.ea..t lo...ong > slo..o..ope down into THE CHASM,... just exactly the reverse of the > great long slope up to the ridge. But we don't get it. All we get > is a 'pdoing!'..or a 'bloop'.
There is no CHASM because the speed of the moving plates is so slow that the vertical effects of the convection are levelled by gravitation.
The reason why I refrained from the tea leaves comparison was that water-saturated tea leaves are denser than water and sink. Only as long as they are dry, they float on the water due to their low density (with air in the pores) and the surface tension (as the dry leaves obviously have positive contact angles - sorry if I don't know the right physics terminology). Wood on water is better, since it is *actually* denser than water (at least for some months) and the contact angle is negative so that surface tension doesn't support them.
> Yes, I know. It's the Earth's centre moving to the crust that's on the > agenda. It's Pteros who want to pull all the crust back down ("where > it never wanted to be") on the grounds that there's far too much heat > (even still) to be accommodated. That is, even though most of the > heat was lost in the beginning to give the differentiated shells - > though they make a distinction between THAT heat, and the heat of > radioactivity which does all the roiling and moiling. That's my > question, which I don't think plate tectonics can answer. HEATLOSS#1 > gives the differentiated shells (gravitational), and puts all the > radioactivity where PTers want it (though it's really concentrated in > the crust). HEATLOSS#2 (which is subordinate to HEATLOSS#1) roils and > moils and breaks up what HEATLOSS#1 put together in the first place. > Since most of the radiogenic heat (#2)has been lost long ago anyhow, > the question is even more pertinent - why is radiogenic heat breaking > up what gravity put together in the first place? And why, if there > is still all that heat, isn't the Earth just bigger (less dense, > ...and forget about the need to convect it all away inside a > 'too-small' Earth?
It's true that there is no agreed conclusion about the prominent heat source. As regards radioactive heat - why does it have to have been consumed soon after the the shell differentiation? As long as there are unstable elements in the rocks, heat will be produced. As regards density: The diameter adjusts to a size where the density of the rock can withstand the pressure produced by gravitation. Very simple. Why does an inflated balloon have a distinct size? The equilibrium will settle where the pressure of the trapped air matches the tension of the rubber. Very simple, isn't it?
> So how then *does plate tectonics reconcile the consanguinity of > transforms globally, with how it sees the segmentation of the crust > into plates? How does it support its position that the plates are > 'independent' of each other (any animation model) with the fact that > their dynamics are clearly tied by transforms? > <http://users.indigo.net.au/don/ee/zip.html>
Which *consanguinity* do you mean? Obviously, differential movement requires a fault, wherever on Earth you look at it. Why do you think the plates are interlocked? I haven't found any evidence of movement parallel to the mid ocean ridges, which would require an interlocking shear force. In the direction rectangular to the ridge, the tensional strength is very small, so the the border between the plates rips apart daily. Gravity prevents a deep gap from being stable, and so firstly, parts of the bordering rock slide into the gap (normal faults), and some of the gap is filled by upwelling magma (which melted due to the released pressure). Obviously, neither detached rocks nor magma has considerable *interlocking* strength - don't know what you're talking about.
> Really, ...I thought your part of the world saw the birth of vertical > tectonics, right back to the early part of the century, with > 'verticalism' continued through the Middle East right into the > Himalayas.....
The vertical movement is a result of the thickening of the continental crust caused by the collision. Continental crust is lighter than the mantle and is pushed upwards if it has become thicker. Plate tectonics is not involved hear - just isostasy.
> And then into the biggest uplift of all - the > Pacific, the one that brought the mantle up, right down to the > transition zone.
Again, I don't know which uplift and gravitational collapse you're speaking of.
Good luck improving your theory and explanations, Christof -- Christof Kuhn Inst. f. Angewandte Geologie, Univ. f. BoKu Wien, Austria
bigdak...@aol.comGetaGrip (Bigdakine) wrote in message <news:20030313234041.27366.00000076@mb-mu.aol.com>... > >Subject: Re: OK - another one for the board > >From: Christof Kuhn Christof.K...@boku.ac.at > >Date: 3/13/03 2:00 PM Hawaiian Standard Time > >Message-id: <3e711bc9$0$13160$3b214...@news.univie.ac.at>
> >Ok - many pters will say, I'm wasting bandwidth (you are not the first > >earth expansionist to deal with fruitlessly here), but here we go.
> >don findlay wrote:
> >> Right, ..I'd forgotten about the ' principle of intercepts'. This is > >> what I mean by distorting mirrors. The POINT:- the Earth is round > >> because gravity rules - it will adjust even half a meter of distortion > >> to zero in a matter of hours (apparently) - and yet Pteros want this > >> curved plate at ridges to flatten off as it migrates across the oceans > >> to arrive at the subduction zone (after millions of years), flat as a > >> tack.
> >Who says that??? Crust is spherical and remains spherical until it is > >deformed at a destructive margin. No need for flatting off. Don't know > >what you speak of.
> My guess is, is that he is butchering the fact that old lithosphere tends not > to obey the depth age relation, it is not as far below sea-level as one might > expect given its age. Some folks refer to this as the flattening of the > lithosphere.
And others would call it isostatic adjustment to expansion. It's all in the Lingo - and the field evidence. At every turn, what's a Puzzle to Pteros, is a lay-down misere to EE-ers. ...PT argues the jargon of the model. EE argues the field evidence.
> As usual, he is not communicating effectively, and you can expect to be > faulted for not understanding him.
Well, let me make myself clear. If there is shrinking (cooling away from ridges) and pushing (ridge-push), how are apportioned:- 1. Depth increase due to gravitational collapse (ridge-push)? 2. Depth increase due to cooling away from the ridges (shrinking)? 3. And what relative weight is given to the simple age-depth relation v. other methods of dating (foraminers; magnetic striping; isotopic ratios), given that they're all incestuously tied? 4. And what does all this mean for the AgeCrustPoster map?
> One can only imagine what happens when something like this goes through the > mind of an EE'er.
At least it stops and rumbles around once it gets in there, which is more than can be said for some Pters, who might as well let suchlike things go straight through, as come up with the easy cut-and-dried, and manifestly false, answers they do - of hot air balloons, pots of soup/ tea/ woodchips-in-a-cauldron, and all the rest. Even your wee googly friend doesn't have much in the way of answers worth a zak when it comes to questions like those above. And I'd put more store in Elvis living, than in the Duelling Propagators people are trying to come up with to explain how ridges grow. Even the Rolling Stones have more craggy geological relevance than anything PT can offer (..trundling around nearly twice as long as GPS, ...and half the folks who don't even know what field evidence is)! D.
>Subject: Re: OK - another one for the board >From: d...@tower.net.au (don findlay) >Date: 3/15/03 3:16 AM Hawaiian Standard Time >Message-id: <5f164087.0303150516.2219d...@posting.google.com>
>bigdak...@aol.comGetaGrip (Bigdakine) wrote in message ><news:20030313234041.27366.00000076@mb-mu.aol.com>... >> >Subject: Re: OK - another one for the board >> >From: Christof Kuhn Christof.K...@boku.ac.at >> >Date: 3/13/03 2:00 PM Hawaiian Standard Time >> >Message-id: <3e711bc9$0$13160$3b214...@news.univie.ac.at>
>> >Ok - many pters will say, I'm wasting bandwidth (you are not the first >> >earth expansionist to deal with fruitlessly here), but here we go.
>> >don findlay wrote:
>> >> Right, ..I'd forgotten about the ' principle of intercepts'. This is >> >> what I mean by distorting mirrors. The POINT:- the Earth is round >> >> because gravity rules - it will adjust even half a meter of distortion >> >> to zero in a matter of hours (apparently) - and yet Pteros want this >> >> curved plate at ridges to flatten off as it migrates across the oceans >> >> to arrive at the subduction zone (after millions of years), flat as a >> >> tack.
>> >Who says that??? Crust is spherical and remains spherical until it is >> >deformed at a destructive margin. No need for flatting off. Don't know >> >what you speak of.
>> My guess is, is that he is butchering the fact that old lithosphere tends >not >> to obey the depth age relation, it is not as far below sea-level as one >might >> expect given its age. Some folks refer to this as the flattening of the >> lithosphere.
>And others would call it isostatic adjustment to expansion.
Why would such an expansion only affect lithosphere greater than 80 myr?
It's all
>in the Lingo - and the field evidence.
You can call a dog's tail a leg.
But that doesn't make it a leg.
A. Lincoln
<snip>
Stuart Dr. Stuart A. Weinstein Ewa Beach Institute of Tectonics "To err is human, but to really foul things up requires a creationist"
Christof Kuhn <Christof.K...@boku.ac.at> wrote in message <news:3e72a977$0$8780$3b214f66@news.univie.ac.at>... > Ok - this shall be my last post in this thread - when I look at your > website, I see that we are talking from two very different points of > knowledge and understanding - one of us got things screwed up, maybe > it's me, but I guess it's you...
Me?...OK Christof, good one. 1 billion Chinese can't be wrong, huh? ...Actually, I've never really thought that much about how plate tectonics rationalises the arcuate shape of the basins in the Western Pacific topologically, since I think basically plate tectonics is quite simply screwed up, with no relevance at all to the Western Pacific margin. I think it's something like this:- http://users.indigo.net.au/don/ee/ngc.html The picture represents the basic geological contour of the Western Pacific margin. The smaller arrows represent the crustal detachment in response to the larger one, which represents in turn the anticlockwise swing of the northern hemisphere (companion clockwise southern hemisphere swing not shown). It's quite easy to visualise, but you have to see that western margin as a ruptured fold, ripped right across the belt. Put your hands out as for the strap, or the cane, like when you were at school (naughty boy), right one beneath the left. Cup them slightly (or maybe arch them - I'm not sure) Now, turn the right one slightly anticlockwise, and push it slightly forward, and you have it. The movement simulates ripping the lower part of the crust off the upper part (or vice versa) - a simple dilating twist. The arcuate shapes are an artifact of boudinage (megaboudinage), which is consequent on folding related to the 'cross-over effect' as the southern hemisphere advances in relation to the north (or again vice versa, with the northern hemisphere in 'retard').. The same movement on a larger scale has widened the whole western Asian region (from the Afghanistan border to the Western Pacific).
...But about the pingpong ball. What you say is quite correct - when you push in a ping pong ball and look at it:- there is the spherical surface, ...there is the downgoing slope, .. and there is the arcuate rim. (I take it you mean that the ball is the oceanic plate, and the dent - if you think of it as infilled with light putty (say) - is the continent.) However, if you reverse the situation and consider the dent as the embryonic ocean floor, ...in other words, migrate the picture back to the onset of ocean floor creation, then the arcuate shape is the other way. The change in the shape of the arc comes when the surface occupied by ocean floor exceeds that of half of the Earth. Bearing in mind that the Western Pacific margin in fact has the **oldest exposure of ocean floor, and therefore most closely represents when the Pacific began to open, I'll leave the implications regarding 'reconfiguration of arc-shape over time', considered when the Pacific margin first split, what it implies for ocean floor growth *and* subduction, for your own consideration, but I think it's a fruitless exercise. (Don't forget either to take into account the 'squirting by extrusion' ("fun tectonics") of the Asian landmass coming the other way too.) (John Hernlund's post)
<More about planes and ping-pong snipped>
> Of course it could be possible that the earth is expanding at the > mid-ocean ridges. But I cannot see any evidence of this.
First order evidence of expansion in the direction of ridge length as regards *continental* expression is in the difference in lengths of the western and eastern Pacific margins, and (in the Indian Ocean) in the separation of Australia/ New Zealand from India. The expression of extension in the *mantle ( along the ridges themselves) is more subtle, but pretty clear, once you see it. Plate tectonics is beginning to attempt weird explanations of this in terms of 'ridge propagation' (but I think they're wrong there (too)). So do plate tectonic classicists, because it screws up nice models of convection. It requires getting **really creative** (**duelling** propagators, no less - if you believe it!! - and why not, it's coming from respectable sources)
As the diameter
> of the Earth grows, the radius of the surface does so too. > Did you ever try to make an orange peel flat? The margin will be torn > resulting in several lobes, so that the peel will loke like a flower in > the end. > Obviously, there are no gaps in the Earth's surface, neither are there > active margins rectangular to the primary active margins, producing the > crust required for the increasing diameter.
This is the southwards wedge-shapes of South America, Africa, and India, like you would get dilating an orange by squeezing an orange on a juicer.
> You write a lot about transform faults - with an expanding earth, the > transform faults could not be parallel, but their distance would have to > grow when you travel away from the "primary" mid-ocean ridge. I cannot > find any occurrence of this feature on the Earth.
Would it change things at all if I showed that they do?. Do you think it would knock a hole in plate tectonics? Can you think of a patch-up job that PT might adopt as a contingency?
> > But hang on, ...you brought up the tea leaf analogy to draw attention > > to the undisturbed surface with all that roiling convection > > underneath. I was just agreeing with you. Anyhow, I haven't thought > > much about it, but a surface tension analogy might not be a bad one. > > That knife edge of a subduction zone looks to me more like a big > > meniscus of a sort, than it does how I would expect a subduction zone > > to look like. How would I expect a big subduction zone to look? > > Something like the inverse of the ridges, i.e. a gre.ea..t lo...ong > > slo..o..ope down into THE CHASM,... just exactly the reverse of the > > great long slope up to the ridge. But we don't get it. All we get > > is a 'pdoing!'..or a 'bloop'.
> There is no CHASM because the speed of the moving plates is so slow that > the vertical effects of the convection are levelled by gravitation.
Right, ...in the same way as the ridges are also levelled by gravitation, except it should be easier to level the ridges because they are *above their gravitational equilibrium. The naturally cooling 'potential chasm' needs to be keep being pushed back up to keep the knife-edged bend of the subduction zone so sharp. But the ridges...for some reason they *keep rising* faster than gravity can *keep levelling* them. This is not an equilibrium condition and implies expansion, unless runaway convection can *keep* sucking it all down faster than gravitational correction can *keep pushing* it (the chasm) back up. (Fun tectonics).
<snip>
> It's true that there is no agreed conclusion about the prominent heat > source. As regards radioactive heat - why does it have to have been > consumed soon after the the shell differentiation? As long as there are > unstable elements in the rocks, heat will be produced.
Half-lives of radiogenic minerals I guess. Half-life of Potassium is xxmy. therefore half of the heat quota is lost in that time - and half of the remainder lost in the next half life etc.
> As regards density: The diameter adjusts to a size where the density of > the rock can withstand the pressure produced by gravitation. Very > simple. Why does an inflated balloon have a distinct size? The > equilibrium will settle where the pressure of the trapped air matches > the tension of the rubber. Very simple, isn't it?
Now this is a good point about the prominent heat source, balloons, convection currents and surface tension. The question is, why does the skin of the Earth confine all this prominent heat, and keep the Earth under such teriffic pressure that convection currents moil, roil, toil and boil beneath it? If the pressure is so great, and the skin cracks open, why doesn't the Earth's size adjust to a lower pressure, ...and get bigger? (No-one seems to want to scale up surface 'tension' (strength of the Earth's crust) as a component in this convectional scenario (say, to compare the traction associated with the battering ram of India with the traction at island arcs). EARTH EXPANSION says that's exactly what **is happening (getting bigger) (but can't explain the source mechanism for expansion). PLATE TECTONICS says that's exactly what is happening too, sort of (excess heat creating ocean floors) (but can't really explain the source mechanism giving 'excess heat'). So they're both really in the same boat, except that PT (geophysics- centred) wants to hang on to subduction (because it wants convection - clever Dick/ model-centred), whilst EE (geology-centred) sees it as entirely unnecessary and wrong, since it conflicts with geological evidence and simple reason.
> > So how then *does plate tectonics reconcile the consanguinity of > > transforms globally, with how it sees the segmentation of the crust > > into plates? How does it support its position that the plates are > > 'independent' of each other (any animation model) with the fact that > > their dynamics are clearly tied by transforms? > > <http://users.indigo.net.au/don/ee/zip.html>
> Which *consanguinity* do you mean? > Obviously, differential movement requires a fault, wherever on Earth you > look at it. > Why do you think the plates are interlocked? I haven't found any > evidence of movement parallel to the mid ocean ridges, which would > require an interlocking shear force. In the direction rectangular to the > ridge, the tensional strength is very small, so the the border between > the plates rips apart daily. Gravity prevents a deep gap from being > stable, and so firstly, parts of the bordering rock slide into the gap > (normal faults), and some of the gap is filled by upwelling magma (which > melted due to the released pressure). > Obviously,
bigdak...@aol.comGetaGrip (Bigdakine) wrote in message <news:20030316044645.04874.00000138@mb-cu.aol.com>... > >Subject: Re: OK - another one for the board > >From: d...@tower.net.au (don findlay) > >Date: 3/15/03 3:16 AM Hawaiian Standard Time > >Message-id: <5f164087.0303150516.2219d...@posting.google.com>
> >bigdak...@aol.comGetaGrip (Bigdakine) wrote in message > ><news:20030313234041.27366.00000076@mb-mu.aol.com>... > >> >Subject: Re: OK - another one for the board > >> >From: Christof Kuhn Christof.K...@boku.ac.at > >> >Date: 3/13/03 2:00 PM Hawaiian Standard Time > >> >Message-id: <3e711bc9$0$13160$3b214...@news.univie.ac.at>
> >> >Ok - many pters will say, I'm wasting bandwidth (you are not the first > >> >earth expansionist to deal with fruitlessly here), but here we go.
> >> >don findlay wrote:
> >> >> Right, ..I'd forgotten about the ' principle of intercepts'. This is > >> >> what I mean by distorting mirrors. The POINT:- the Earth is round > >> >> because gravity rules - it will adjust even half a meter of distortion > >> >> to zero in a matter of hours (apparently) - and yet Pteros want this > >> >> curved plate at ridges to flatten off as it migrates across the oceans > >> >> to arrive at the subduction zone (after millions of years), flat as a > >> >> tack.
> >> >Who says that??? Crust is spherical and remains spherical until it is > >> >deformed at a destructive margin. No need for flatting off. Don't know > >> >what you speak of.
> >> My guess is, is that he is butchering the fact that old lithosphere tends > not > >> to obey the depth age relation, it is not as far below sea-level as one > might > >> expect given its age. Some folks refer to this as the flattening of the > >> lithosphere.
> >And others would call it isostatic adjustment to expansion.
> Why would such an expansion only affect lithosphere greater than 80 myr?
It doesn't.. I think I can see it ok in the ridge - transform sectors too, but not as 'propagators'. I need to work out how best to clarify it though (still mulling). D.
On 16 Mar 2003 06:51:28 -0800, d...@tower.net.au (don findlay) wrote:
<snip>
><snip>
>> It's true that there is no agreed conclusion about the prominent heat >> source. As regards radioactive heat - why does it have to have been >> consumed soon after the the shell differentiation? As long as there are >> unstable elements in the rocks, heat will be produced.
>Half-lives of radiogenic minerals I guess. Half-life of Potassium is >xxmy. therefore half of the heat quota is lost in that time - and half >of the remainder lost in the next half life etc.
I am still at a loss as to how Plate Tectonics gets rid of all the sediment from continental erosion. Most, if not all, PT animations have the Philippines, Southern Alaska cross subduction zones, unscathed. The explanation is lighter material is NOT subducted. Yet, it seems, subduction can pull down the sediment in the ocean with no problem.
half life of Potassium-40 (about 1.3 billion years) half-life of thorium-232 76,000 years half-life of Uranium 238 4.5 billion years half-life of Uranium 234 245,00 years http://www.ccnr.org/decay_U238.html#HL
Number of half lives in 4.6by: half life of Potassium-40 (about 1.3 billion years)/ 4.6by = 3.5 times more half-life of thorium-232 76,000 years/ 4.6by = 60526 times more half-life of Uranium 238 4.5 billion years/ 4.6by = 1 times more half-life of Uranium 234 245,00 years/ 4.6by = 18775 times more
then the subduction rates would be considerably greater in the past then in the present. Assuming heat is placing the material and it needs to be removed to keep a constant radius.
Yet current rates of erosion indicate the volume of the continents above sea level would be eroded away in 25-40my. Even with the iceberg continuing to rise, due to buoyancy, above the level of the sea, it will also be eroded without material being added.
So if currently, the rate of all ocean crust removal is 200my and taking all the sediment, how is it the continents survive being subducted, but the sediment eroded from them, does not?
It would seem the recycle rate is not with the surface and the mantle, but the continents and ocean.
Actually this is a problem for both Expanding Earth and Plate Tectonics.
The erosion rate is known, the replenishment rate needs to equal.
> On 16 Mar 2003 06:51:28 -0800, d...@tower.net.au (don findlay) wrote:
> <snip> > ><snip>
> >> It's true that there is no agreed conclusion about the prominent heat > >> source. As regards radioactive heat - why does it have to have been > >> consumed soon after the the shell differentiation? As long as there are > >> unstable elements in the rocks, heat will be produced.
> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is > >xxmy. therefore half of the heat quota is lost in that time - and half > >of the remainder lost in the next half life etc.
> I am still at a loss as to how Plate Tectonics gets rid of all the > sediment from continental erosion. Most, if not all, PT animations > have the Philippines, Southern Alaska cross subduction zones, > unscathed. The explanation is lighter material is NOT subducted. Yet, > it seems, subduction can pull down the sediment in the ocean with no > problem.
It isn't sediment that gets pulled down. It is the basalt which formed at the mid ocean ridges, and on which the sediment collects.
>> >> It's true that there is no agreed conclusion about the prominent heat >> >> source. As regards radioactive heat - why does it have to have been >> >> consumed soon after the the shell differentiation? As long as there are >> >> unstable elements in the rocks, heat will be produced.
>> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is >> >xxmy. therefore half of the heat quota is lost in that time - and half >> >of the remainder lost in the next half life etc.
>> I am still at a loss as to how Plate Tectonics gets rid of all the >> sediment from continental erosion. Most, if not all, PT animations >> have the Philippines, Southern Alaska cross subduction zones, >> unscathed. The explanation is lighter material is NOT subducted. Yet, >> it seems, subduction can pull down the sediment in the ocean with no >> problem.
>It isn't sediment that gets pulled down. It is the basalt which formed at >the mid ocean ridges, and on which the sediment collects.
But if the sediment is not being subducted, then it should be collecting at subduction zones. There are estimates the total sediment on all the oceans floors is about twice the volume of material on all the continents above sea level.
If this is what has collected in 200my, where is the sediment for all the subduction cycles before?
>Subject: Re: OK - another one for the board >From: J. Taylor j...@gorge.NOSPAM.net >Date: 3/17/03 4:03 AM Hawaiian Standard Time >Message-id: <2mkb7vcc38vr9ldjtflb5df9ordv30i...@4ax.com>
>>> >> It's true that there is no agreed conclusion about the prominent heat >>> >> source. As regards radioactive heat - why does it have to have been >>> >> consumed soon after the the shell differentiation? As long as there are >>> >> unstable elements in the rocks, heat will be produced.
>>> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is >>> >xxmy. therefore half of the heat quota is lost in that time - and half >>> >of the remainder lost in the next half life etc.
>>> I am still at a loss as to how Plate Tectonics gets rid of all the >>> sediment from continental erosion. Most, if not all, PT animations >>> have the Philippines, Southern Alaska cross subduction zones, >>> unscathed. The explanation is lighter material is NOT subducted. Yet, >>> it seems, subduction can pull down the sediment in the ocean with no >>> problem.
>>It isn't sediment that gets pulled down. It is the basalt which formed at >>the mid ocean ridges, and on which the sediment collects.
>But if the sediment is not being subducted, then it should be >collecting at subduction zones.
Some sediment is being subducted.The evidence for this found in the distribution of isotopes found in Island Arc lavas. In other cases it is piled up. Do a google search on *accretionary wedges*.
Why do you constantly ask questions that any sophomore geology major can answer? Do yourself a favor and google (or better yet, visit a library) before you ask.
Stuart
Dr. Stuart A. Weinstein Ewa Beach Institute of Tectonics "To err is human, but to really foul things up requires a creationist"
> >> >> It's true that there is no agreed conclusion about the prominent heat > >> >> source. As regards radioactive heat - why does it have to have been > >> >> consumed soon after the the shell differentiation? As long as there are > >> >> unstable elements in the rocks, heat will be produced.
> >> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is > >> >xxmy. therefore half of the heat quota is lost in that time - and half > >> >of the remainder lost in the next half life etc.
> >> I am still at a loss as to how Plate Tectonics gets rid of all the > >> sediment from continental erosion. Most, if not all, PT animations > >> have the Philippines, Southern Alaska cross subduction zones, > >> unscathed. The explanation is lighter material is NOT subducted. Yet, > >> it seems, subduction can pull down the sediment in the ocean with no > >> problem.
> >It isn't sediment that gets pulled down. It is the basalt which formed at > >the mid ocean ridges, and on which the sediment collects.
> But if the sediment is not being subducted, then it should be > collecting at subduction zones. There are estimates the total > sediment on all the oceans floors is about twice the volume of > material on all the continents above sea level.
> If this is what has collected in 200my, where is the sediment for all > the subduction cycles before?
LOL, yes you caught me out there! Of course there is very little continental sediment being produced from the Phiippines, and even less in the Aleutians, so their trenches are going to be pretty empty.
Most of the sediment is flowing onto the passive margins in the Atlantic, because the subduction of the Pacific Plate is building the Andes and Rockies which block the flow of rivers on the American continets in to that ocean.
> >> >> It's true that there is no agreed conclusion about the prominent heat > >> >> source. As regards radioactive heat - why does it have to have been > >> >> consumed soon after the the shell differentiation? As long as there are > >> >> unstable elements in the rocks, heat will be produced.
> >> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is > >> >xxmy. therefore half of the heat quota is lost in that time - and half > >> >of the remainder lost in the next half life etc.
> >> I am still at a loss as to how Plate Tectonics gets rid of all the > >> sediment from continental erosion. Most, if not all, PT animations > >> have the Philippines, Southern Alaska cross subduction zones, > >> unscathed. The explanation is lighter material is NOT subducted. Yet, > >> it seems, subduction can pull down the sediment in the ocean with no > >> problem.
> >It isn't sediment that gets pulled down. It is the basalt which formed at > >the mid ocean ridges, and on which the sediment collects.
> But if the sediment is not being subducted, then it should be > collecting at subduction zones. There are estimates the total > sediment on all the oceans floors is about twice the volume of > material on all the continents above sea level.
> If this is what has collected in 200my, where is the sediment for all > the subduction cycles before?
> JT >The sediments on oceanic crust being subducted gets carried down with the
oceanic crust. Oceanic sediments tend to be thin as compared to continental edge sediments.
Don't be so thick headed, I've been ignoring the thread the best I could so I can't be sure, but I doubt if anyone said oceanic sediments don't get subducted in trench bottoms. As for continental sediments I doubt anyone said none ever get subducted either. Just look around you, we don't seem to have wads of sediments around oceanic trenches, but when continents get involved you end up with wads of twisted continental sediment and oceanic material plastered on the edges. I'm sure the sunny state of California, where I sit today, owes much of its uniqueness (strangeness ") to such goings on ;-)
J. Taylor <j...@gorge.NOSPAM.net> wrote in message <news:2mkb7vcc38vr9ldjtflb5df9ordv30irtf@4ax.com>... > On Mon, 17 Mar 2003 10:56:16 -0000, "Alastair McDonald" > <abbe...@abbemac.leavethisout.fsnet.co.uk> wrote:
> >> >> It's true that there is no agreed conclusion about the prominent heat > >> >> source. As regards radioactive heat - why does it have to have been > >> >> consumed soon after the the shell differentiation? As long as there are > >> >> unstable elements in the rocks, heat will be produced.
> >> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is > >> >xxmy. therefore half of the heat quota is lost in that time - and half > >> >of the remainder lost in the next half life etc.
> >> I am still at a loss as to how Plate Tectonics gets rid of all the > >> sediment from continental erosion. Most, if not all, PT animations > >> have the Philippines, Southern Alaska cross subduction zones, > >> unscathed. The explanation is lighter material is NOT subducted. Yet, > >> it seems, subduction can pull down the sediment in the ocean with no > >> problem.
> >It isn't sediment that gets pulled down. It is the basalt which formed at > >the mid ocean ridges, and on which the sediment collects.
> But if the sediment is not being subducted, then it should be > collecting at subduction zones. There are estimates the total > sediment on all the oceans floors is about twice the volume of > material on all the continents above sea level.
> If this is what has collected in 200my, where is the sediment for all > the subduction cycles before?
I've been doing a bit of studying (reading books). Let me clarify. You can best understand this 'wet-sediment scrape-off' in terms of what's called 'accretionary wedges'. Accretionary wedges happen where a continent gets plastered with wet sediment as the mantle deposits its little grey load before wilting (down a subduction zone). Since the mantle itself is pretty soft, this is best done if a hard continent can be used as a battering ram. A good example is India. India used to be much further south, with an ocean called the Tethys between it and the landmass of Asia to the north This 'Tethys' began to get closed up by the advance of a convecting cell carrying India with it from the south. A subduction zone developed (plunging northwards) along the junction of the tethys and this northern continent, and, as the mantle descended, aa..aaall the sediment from the floor of this ocean-cell began to get scraped off and 'plastered' on to Asia. This went on for a while and culminated with India being rammed into the whole lot. You can still see the 'stuttering' effect of this ramming, the way the contours are rippled (something like shock waves), imprinted, on the Asian Landmass all the way to the Okhotsk Peninsula, where the recoil ripped off the penisula, and swung it over the whole Russian landmass. Further south it squirted the whole Tethys sideways (westwards). So you can see the fantastic effect all this 'grunt' of convection can have, even though it's so slow, and the mantle is pretty soft.
All the volcanoes all the way along the subduction zone of what is now the Himalayas are testimony to the importance of pore geometry and matrix dihedral angle equilibrium conditions that controlled fluid migration and magmatism during wet-sediment scrape-off. Yes, I know a lot of the Himalayas are pretty flat, but a well known feature of accretionary wedges is that pull-apart structures happen right on the crests of the folds whilst these are compressing. This is known as 'synorogenic extension' . So the wedge is not just squirting out to the east, towards the western Pacific, it is also splurging south, towards India. This is why plate tectonics is such a comprehensively excellent model for understanding geotectonics, and offering so much scope for future research.
Hope this clarifies your question about volume. df. (PS you should do more reading. It's very illuminating!)
>>Subject: Re: OK - another one for the board >>From: J. Taylor j...@gorge.NOSPAM.net >>Date: 3/17/03 4:03 AM Hawaiian Standard Time >>Message-id: <2mkb7vcc38vr9ldjtflb5df9ordv30i...@4ax.com>
>>>> >> It's true that there is no agreed conclusion about the prominent heat >>>> >> source. As regards radioactive heat - why does it have to have been >>>> >> consumed soon after the the shell differentiation? As long as there are >>>> >> unstable elements in the rocks, heat will be produced.
>>>> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is >>>> >xxmy. therefore half of the heat quota is lost in that time - and half >>>> >of the remainder lost in the next half life etc.
>>>> I am still at a loss as to how Plate Tectonics gets rid of all the >>>> sediment from continental erosion. Most, if not all, PT animations >>>> have the Philippines, Southern Alaska cross subduction zones, >>>> unscathed. The explanation is lighter material is NOT subducted. Yet, >>>> it seems, subduction can pull down the sediment in the ocean with no >>>> problem.
>>>It isn't sediment that gets pulled down. It is the basalt which formed at >>>the mid ocean ridges, and on which the sediment collects.
>>But if the sediment is not being subducted, then it should be >>collecting at subduction zones.
>Some sediment is being subducted.The evidence for this found in the >distribution of isotopes found in Island Arc lavas. In other cases it is piled >up. Do a google search on *accretionary wedges*.
>Why do you constantly ask questions that any sophomore geology major can >answer?
Well go ahead and ask your sophomore geology major, most people get basic math in about the second grade.
Now little Stuey if we put in 5 units of sediment, but only take 3 out how much sediment is still left?
>"J. Taylor" <j...@gorge.NOSPAM.net> wrote in message >news:2mkb7vcc38vr9ldjtflb5df9ordv30irtf@4ax.com... >> On Mon, 17 Mar 2003 10:56:16 -0000, "Alastair McDonald" >> <abbe...@abbemac.leavethisout.fsnet.co.uk> wrote:
>> >> >> It's true that there is no agreed conclusion about the prominent >heat >> >> >> source. As regards radioactive heat - why does it have to have been >> >> >> consumed soon after the the shell differentiation? As long as there >are >> >> >> unstable elements in the rocks, heat will be produced.
>> >> >Half-lives of radiogenic minerals I guess. Half-life of Potassium is >> >> >xxmy. therefore half of the heat quota is lost in that time - and half >> >> >of the remainder lost in the next half life etc.
>> >> I am still at a loss as to how Plate Tectonics gets rid of all the >> >> sediment from continental erosion. Most, if not all, PT animations >> >> have the Philippines, Southern Alaska cross subduction zones, >> >> unscathed. The explanation is lighter material is NOT subducted. Yet, >> >> it seems, subduction can pull down the sediment in the ocean with no >> >> problem.
>> >It isn't sediment that gets pulled down. It is the basalt which formed >at >> >the mid ocean ridges, and on which the sediment collects.
>> But if the sediment is not being subducted, then it should be >> collecting at subduction zones. There are estimates the total >> sediment on all the oceans floors is about twice the volume of >> material on all the continents above sea level.
>> If this is what has collected in 200my, where is the sediment for all >> the subduction cycles before?
>> JT >>The sediments on oceanic crust being subducted gets carried down with the >oceanic crust. Oceanic sediments tend to be thin as compared to continental >edge sediments.
Even if it is thin, it is light in comparison to the ocean crust. How is it pulled down with the crust? Would not the natural buoyancy of the material resist being pulled down, especially since the rate of subduction is so slow?
>Don't be so thick headed, I've been ignoring the thread the best I could so >I can't be sure, but I doubt if anyone said oceanic sediments don't get >subducted in trench bottoms.
Nobody said it did not get subducted. I was just curious as to how a land mass can cross a subduction zone, due to its natural buoyancy, but the sediment eroded from it is not subject to the same fate.
>As for continental sediments I doubt anyone >said none ever get subducted either.
The point is not that none ever gets subducted,, but ALL must be, otherwise the sediment will accumulate.
>Just look around you, we don't seem to >have wads of sediments around oceanic trenches,
See there you are, it must be all subducted, but then there is the little problem of land masses which can float across and not be subducted.
> but when continents get >involved you end up with wads of twisted continental sediment and oceanic >material plastered on the edges. I'm sure the sunny state of California, >where I sit today, owes much of its uniqueness (strangeness ") to such >goings
Then North America subducted the subduction zone before swallowing the spreading ridge?
In article <20030317144924.27803.00000...@mb-cg.aol.com>,
bigdak...@aol.comGetaGrip (Bigdakine) wrote: > Some sediment is being subducted.The evidence for this found in the > distribution of isotopes found in Island Arc lavas. In other cases it is piled > up. Do a google search on *accretionary wedges*.
In some places, such as the Marianas, where coupling is low and there are no giant earthquakes, *all* the sediment is being subducted. There there is no accretionary wedge at all, and the fluids venting in the forearc reflect the chemistry of the subducting plate.
In other places, such as much of Peru-Chile, where the coupling is high and earthquakes can be monsters, the downgoing plate is nibbling away at the underside of the overriding plate. There is an accretionary wedge, but the sediments are all derived from the continent. That's how you get the Palaeozoics outcropping along the coast, despite the longevity of the Peru-Chile system. It's worth noting too that those Palaeozoics shoot the expanding Earth right out of the water because they deny a match between eastern Australia and the west coast of South America. Needless to say the EEers ignore them...
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