Jump to content
arc

Plate tectonic mechanism ?

Recommended Posts

The problem with arc's "theory" is that it is only a conceptual model. The "changes" arc has made to it is simply to take the words that others have given him, like "strain energy" and to substitute them into his thesis in place of the previous less technical words. In reality, the conceptual model did not change.

Edited by billiards

Share this post


Link to post
Share on other sites

Well, I’m back, although I have been periodically sneaking in here rather regularly for a needed SFN fix. My time away has given me an opportunity to think through what Studiot had said about this model;

 

"Finally the important idea that an unconfined body suffers no stress on thermal expansion."

 

I am still defining the processes in regards to the mantle’s outward displacement and how it provides shear stresses that could fracture a large expansive plate section, such as an oceanic plate, breaking it free of its source, from its parental continental land mass if you will, when that oceanic plate’s expanse reaches a critical point in its gradual and periodically increasing width.

 

And I am still also defining in regards to the division of a large continental plate, processed through many cycles that can weaken and then eventually divide it into two retreating halves separated by a newly formed divergent boundary, as was the case with the Atlantic Ocean.

 

These continental land masses extend into the mantle much deeper than the oceanic plates and provide their adjacent and still connected oceanic plate sections an adequate anchor point, as does any subduction into a trench for that matter, for a growing oceanic plate extending out to its divergent boundary.

 

An “unconfined body“ in regards to this model would be any plate not connected to a large continental plate and/or one that is not subducting into a trench. Not too many of those around these days.

 

This arrangement of large continental plates being rather grounded like a ship on a sand bar in relation to the mantle provides the mechanism that defines the reason for the differences between the various global divergent boundary metrics. It is simply the result of that distance from the divergent boundary edge and that rather immobile anchor point that requires the plate edge at the divergent boundary to proportionally withdraw or recede as the mantle displaces outward beneath it, as can be seen happening at all divergent boundaries currently.

 

You can simulate this movement in a very simple demonstration by taping several strips of different lengths of a very light paper or ribbon to a child’s playground rubber ball. With only one end of the strip taped stationary the other ends that are free to move will show a proportional movement to their particular length when air is added or removed from the ball. The longer strip will show the most movement. If one strip is twice as long as the other one its loose end will move twice as far as the other one when the ball’s radius is changed.

 

A subtle but proportionate shear force applied to an unusually wide ocean or even continental plate from this model’s mantle displacement scenario, seems reasonable due to the current model’s claim that the movement and interaction between hypothesized convection cells within the mantle and the tectonic plate above it purportedly provides the observed plate movement and subsequent subduction. This would require a degree of traction between the crustal plate and the convecting mantle material.

 

The standard model relies on a coupling between the mantle and the mobile crust. The current model suggests that the convecting mantle material pulls or rather coaxes the crust in the direction that the convective current is traveling, leading to statements such as;

 

http://people.earth.yale.edu/sites/default/files/files/Bercovici/51EPSL-Frontiers-PlateGen.pdf

 

One drawback of this approach is that it must prescribe a fault instead of letting it arise and evolve from the physics of the system; thus, for example, it cannot account for how a fault or weak zone is formed in lithosphere that is newly created at ridges. Nevertheless, these studies have clearly demonstrated that without low-friction, fault-like concentrations of deformation, called ‘shear localizations’, simple fluid behavior cannot generate plate-like motion.

 

While in this model the mantle displaces outward causing the ocean plate that is secured to the continent, or even through subduction, to be shortened at its divergent boundary end. This interaction between the crust and mantle would involve a given degree of resistance between the two as the crust slides on top of the mantle relieving the stresses in a subtle ebb and flow of tension and then dissipation.

 

And as the oceanic plate gradually lengthens this resistance metric should increase in proportion. It would then seem reasonable that the oceanic plate would eventually fracture and separate when this resistance multiplies to a critical level.

 

The fracture would be where this strain was greatest, which would be the farthest distance possible from the divergent boundary, and interestingly where many structural failures commonly occur in manufactured assemblies, where a more flexible element transitions to an immobile and ridged base. It appears that oceanic plates fracture quite close to their associated continental origin in this manner.

 

These fractures though are likely initiated during the preceding period of extreme crustal compression when the mantle had receded and substantial compression has accumulated in the crust. A large oceanic plate extending out from a large continent would be providing substantial leverage to its continental margin that a shorter plate would not achieve.

 

So it would then seem likely the plate is at least partially broken before the mantle begins extending outward and providing the shear stresses that will open these breaks and process these faults into convergent boundaries over many following cycles.

 

In an ideal model the crust would be uniform in its structure like the one that I described in post #349 or Studiot described in post #358 below.

 

2) Following your scenario the Earth expands to radius R1, straining the periphery as shown in the equations and inducing a peripheral hoop tensile stress. In my simple model there are no shear stresses at this point.

 

3) At some point in the expansion this peripheral stress is sufficient to fracture the crust by cracking. Since the crust is no longer continuous the hoop stress is relaxed. (I have simplified this to zero). This relaxation induces shear stresses between the crust and the supporting interior. The shortening of the old crust leaves gaps in the periphery.

 

But in reality the crust resembles something that has been broken and shoddily repaired repeatedly for several billion years, exhibiting structural weaknesses at every location and at every depth. It is a chipboard planet, and a composite supercontinent like Pangaea or even a large continent with an adjoining oceanic crust such as North America with its adjoined Atlantic oceanic plate section, is no match for the continuous cycles of the displacing mantle.

 

North America and its Atlantic plate section extend 7456 km +/- from just the California coast alone to the Atlantic mid-ocean ridge. That is nearly one fifth of the planet’s circumference measured at the equator. The southwest is exhibiting the results of being extended at the Basin and Range Provence some 10 – 20 MYA at the continent’s western margin.

 

Currently the area under the Mississippi river valley is now showing evidence by way of the Reelfoot Rift that periodic shear stresses on the N.A. plate are being reapplied during this most recent period of mantle displacement. Referring back to that rubber ball; wet a long strip of that tissue paper and smooth it onto the ball. Now add air and watch it tear in half near its center. This area is receiving shear stress levels that are to low to separate the continent but high enough to thin the over riding continent at this very old weak point.

 

post-88603-0-23188900-1422857696_thumb.png

 

Image above was furnished through and in no way endorsed by http://www.geomapapp.orgusing Global Multi-Resolution Topography (GMRT) Synthesis,

Ryan, W. B. F., S.M. Carbotte, J. Coplan, S. O'Hara, A. Melkonian, R. Arko, R.A. Weissel, V. Ferrini, A. Goodwillie, F. Nitsche, J. Bonczkowski, and R. Zemsky (2009), Global Multi-Resolution Topography (GMRT) synthesis data set, Geochem. Geophys. Geosyst., 10, Q03014, doi:10.1029/2008GC002332.

Data doi: 10.1594/IEDA.0001000, through http://creativecommons.org/licenses/by-nc-sa/3.0/us/

 

http://neic.usgs.gov/neis/eq_depot/2003/eq_030606/

 

The earthquakes of the New Madrid seismic zone occur within a large network of faults called the Reelfoot rift. The rift formed about 500 million years ago, when this region was stretched in the northwest-southeast direction. Along a northeast-southwest zone at least 70 km (40 mi) wide and 500 km (300 mi) long, the rocks in the rift were slowly dropped down about 1-2 km (1 mi) along some of the faults. Now the region is undergoing east- west shortening, and the ancient faults of the Reelfoot rift are being reactivated to generate earthquakes.

 

post-88603-0-17599000-1422858043_thumb.jpg

 

“The rift formed about 500 million years ago, when this region was stretched in the northwest-southeast direction.”

 

http://www.uc.edu/news/NR.aspx?id=13782

Attila Kilinc, professor of geochemistry explains that the New Madrid fault zone is not a single crack threading through the central U.S. – but that tens and sometimes hundreds of fault lines are running parallel to each other for about 125 miles from Arkansas to Illinois. Because these faults are not exposed at the surface, it’s very difficult to make measurements of movement, and it’s difficult to forecast on which fault the next earthquake might nucleate.

 

post-88603-0-94509300-1422858269_thumb.jpg

 

It is likely that the Reelfoot rift was just one of the several other rifts on that Supercontinent that appeared on either side of the one that eventually formed the Atlantic basin, and as these cycles continued the Atlantic oceanic plate continued to gain material and increase the stresses being imposed onto the Reelfoot rift.

 

Image below was furnished through and in no way endorsed by http://www.geomapapp.orgusing Global Multi-Resolution Topography (GMRT) Synthesis,

Ryan, W. B. F., S.M. Carbotte, J. Coplan, S. O'Hara, A. Melkonian, R. Arko, R.A. Weissel, V. Ferrini, A. Goodwillie, F. Nitsche, J. Bonczkowski, and R. Zemsky (2009), Global Multi-Resolution Topography (GMRT) synthesis data set, Geochem. Geophys. Geosyst., 10, Q03014, doi:10.1029/2008GC002332.

Data doi: 10.1594/IEDA.0001000, through http://creativecommons.org/licenses/by-nc-sa/3.0/us/

 

post-88603-0-86729900-1422859083_thumb.jpg

 

Above is a typical cross section of the Atlantic Ocean basin. You can see the high level of compression that it is subjected to. These two halves that make up this cross section are directly connected to their respective continents, North America to the left and Northern Africa to the right. This boundary is compressed not only by the mass of those two continents but the entire global plate matrix, to the point that it moved vertically to relieve the stresses applied to it.

 

The Atlantic oceanic plate will respond as a stress relieving mechanism by shifting towards the N.A. continent and expending its gravitational potential energy as kinetic movement when the mantle displaces outward, thus explaining the previously sited observation;

 

http://neic.usgs.gov/neis/eq_depot/2003/eq_030606/

The earthquakes of the New Madrid seismic zone occur within a large network of faults called the Reelfoot rift. The rift formed about 500 million years ago, when this region was stretched in the northwest-southeast direction. Along a northeast-southwest zone at least 70 km (40 mi) wide and 500 km (300 mi) long, the rocks in the rift were slowly dropped down about 1-2 km (1 mi) along some of the faults. Now the region is undergoing east- west shortening, and the ancient faults of the Reelfoot rift are being reactivated to generate earthquakes.

 

The Atlantic oceanic plate is responding to the changes at the Reelfoot Rift. As the mantle displaces outward, as is currently predicted by this model, the Atlantic oceanic plate will partially relieve the now declining gravitational potential derived compression at the Reelfoot rift.

 

The GPE seen in that graph above will shift its potential energy of the Atlantic oceanic plate to the N.A. continent as N.A. moves in tandem with the displacing mantle, producing this most recent seismic activity that began in the early 1800’s when this current period of activity started.

 

This movement is of course tied to the overall westward mechanical advancement of the N.A. continent that is driven by the tremendous amounts of GPE from millions of years’ worth of divergent boundary infill that will be continually utilized to move the continent to the west. And when the mantle again recedes in great measure millions of years from now the resulting increased compression will of course once again overwhelm and raise the Atlantic mid-ocean ridge.

 

I'm sorry this was so long but I needed to outline this model's current dynamics compared to that simple "minimalist approach" that gave a simple example of the beginning dynamics for plate tectonics to originally start from.

 

My daughter is getting married next Sunday so it is going to be a busy time for us, I will try to stay in touch.

 

Share this post


Link to post
Share on other sites

post-88603-0-86729900-1422859083_thumb.j

Above is a typical cross section of the Atlantic Ocean basin. You can see the high level of compression that it is subjected to. These two halves that make up this cross section are directly connected to their respective continents, North America to the left and Northern Africa to the right. This boundary is compressed not only by the mass of those two continents but the entire global plate matrix, to the point that it moved vertically to relieve the stresses applied to it.

Arc, could you please explain where the compression is in this diagram. I assume you mean in the middle, but it would help if you clarify this point.

Share this post


Link to post
Share on other sites

Arc, could you please explain where the compression is in this diagram. I assume you mean in the middle, but it would help if you clarify this point.

 

 

 

attachicon.gifAtlantic cross section.jpg

 

Above is a typical cross section of the Atlantic Ocean basin. You can see the high level of compression that it is subjected to. These two halves that make up this cross section are directly connected to their respective continents, North America to the left and Northern Africa to the right. This boundary is compressed not only by the mass of those two continents but the entire global plate matrix, to the point that it moved vertically to relieve the stresses applied to it.

 

There is currently no compression directly related to the mantle's subsidence in that diagram and there has not been any since that boundary ruptured and created that rather grand mountain range. There is I'm sure some compression at the base of that now raised mass where prior there was a much lower amount when it was a more modest ridge section similar to most other Mid-ocean ridge sections.

 

This model proposes that mountain building has only occurred at specific times throughout geologic history. The last one occurred approximately 5 MYA. I would say this structure dates to that period. It takes massive amounts of GPE to overrun the convergent boundaries rates of resistance and redirect this energy to rupture already vulnerable areas like the convergent boundary of the Himalayas or a divergent boundary like that of the Mid Atlantic ridge. This is about crushing them with the GPE of large continents when the mantle recedes, releasing more kinetic energy than can be processed into convergent trenches.

 

ANNALS OF GEOPHYSICS, SUPPLEMENT TO VOL. 49, N. 1, 2006

Mountain uplift and the Neotectonic Period

CLIFF D. OLLIER

School of Earth and Geographical Sciences, University of Western Australia, Perth, Australia

9.2. EXAMPLES

9.2.1. Tibet, Himalayas, Kunlun Mountains

(As an example, consider the timing of uplift in Tibet and its bordering mountains. Gansser (1991) wrote: «... we must realize that the morphogenic phase is not only restricted to the Himalayas but involves the whole Tibetan block. This surprising fact shows that an area of 2500000 km2 has been uplifted 3000-4000 m during Pleistocene time and that this uplift is still going on.» In places the uplift rate is 4.5 mm/yr (five times the maximum in the European Alps). According to Wu et al. (2001) from the Pliocene to the Early Quaternary (5-1.1 Million years) the Kunlun Pass area of the Tibetan Plateau was no more than 1500 m high and was warm and humid. They write: «The extreme geomorphic changes in the Kunlun Pass area reflect an abrupt uplift of the Tibet Plateau during the Early and Middle Pleistocene. The Kunlun-Yellow River tectonic movement occurred 1.1-0.6 Million years.» Zheng et al. (2000) concluded from sediments at the foot of the Kunlun Mountains that uplift began around 4.5 Million years.)

 

9.4. CONCLUSIONS

(Mountains are created by the vertical uplift of former plains, independent of any folding of the rocks underneath. The age of mountains should therefore refer to the age of vertical uplift after planation, not to the last period of folding (if the underlying bedrock happens to be folded). Most uplift occurred in the Plio-Pleistocene, or the very Late Miocene. The Neotectonic Period is demonstrated by the large amount of work listed in table 9.I. Plate tectonics, the ruling theory of the past forty years, has no adequate explanation for the widespread planation in mountain regions, or the remarkably young uplift. Indeed it is based on an association of folding and uplift that is demonstrably untrue. Plate tectonics has no plausible explanation for mountains on passive margins or continental interiors. From now on it is incumbent on those who propose models of mountain formation to do two things: Incorporate planation surfaces into the story (or prove there was no former planation). – Either disprove the Neotectonic Period hypothesis, or show how their proposed mechanisms fit into the time scale of just a few million years). . . . .(Uplift occurred over a relatively short and distinct time. Some unknown process created mountains after a period with little or no significant uplift. This is a deviation from uniformitarianism. The mountain building period is relatively short, and not on the same time scale as granite intrusion (which takes tens of millions of years), or plate tectonics which is supposedly continuous over hundreds of millions of years. The same rapid uplift occurs in areas where hypotheses such as mantle plumes are not appropriate. We do not yet know what causes this short, sharp period of uplift, but we can exclude naive mountain-building hypotheses that are on the wrong time scale.)

 

 

 

Edited by arc

Share this post


Link to post
Share on other sites

Good Morning, I hope the wedding went well.

 

Back to geology;

 

 

arc

You can see the high level of compression that it is subjected to

 

Billiards

Arc, could you please explain where the compression is in this diagram. I assume you mean in the middle, but it would help if you clarify this point.

 

arc

There is currently no compression directly related to the mantle's subsidence in that diagram and there has not been any since that boundary ruptured and created that rather grand mountain range. There is I'm sure some compression at the base of that now raised mass where prior there was a much lower amount when it was a more modest ridge section similar to most other Mid-ocean ridge sections.

 

I'm sorry I find that explanation as clear as mud.

 

Perhaps you mean former compression?

Otherwise you need to account for the fact that the Atlantic floor is currently widening and cannot therefore be in compression, rather than tell us about the Himalayas whcih are not in your section.

Share this post


Link to post
Share on other sites

There is currently no compression directly related to the mantle's subsidence in that diagram and there has not been any since that boundary ruptured and created that rather grand mountain range. There is I'm sure some compression at the base of that now raised mass where prior there was a much lower amount when it was a more modest ridge section similar to most other Mid-ocean ridge sections.

 

This model proposes that mountain building has only occurred at specific times throughout geologic history. The last one occurred approximately 5 MYA. I would say this structure dates to that period. It takes massive amounts of GPE to overrun the convergent boundaries rates of resistance and redirect this energy to rupture already vulnerable areas like the convergent boundary of the Himalayas or a divergent boundary like that of the Mid Atlantic ridge. This is about crushing them with the GPE of large continents when the mantle recedes, releasing more kinetic energy than can be processed into convergent trenches.

 

ANNALS OF GEOPHYSICS, SUPPLEMENT TO VOL. 49, N. 1, 2006

Mountain uplift and the Neotectonic Period

CLIFF D. OLLIER

School of Earth and Geographical Sciences, University of Western Australia, Perth, Australia

9.2. EXAMPLES

9.2.1. Tibet, Himalayas, Kunlun Mountains

(As an example, consider the timing of uplift in Tibet and its bordering mountains. Gansser (1991) wrote: «... we must realize that the morphogenic phase is not only restricted to the Himalayas but involves the whole Tibetan block. This surprising fact shows that an area of 2500000 km2 has been uplifted 3000-4000 m during Pleistocene time and that this uplift is still going on.» In places the uplift rate is 4.5 mm/yr (five times the maximum in the European Alps). According to Wu et al. (2001) from the Pliocene to the Early Quaternary (5-1.1 Million years) the Kunlun Pass area of the Tibetan Plateau was no more than 1500 m high and was warm and humid. They write: «The extreme geomorphic changes in the Kunlun Pass area reflect an abrupt uplift of the Tibet Plateau during the Early and Middle Pleistocene. The Kunlun-Yellow River tectonic movement occurred 1.1-0.6 Million years.» Zheng et al. (2000) concluded from sediments at the foot of the Kunlun Mountains that uplift began around 4.5 Million years.)

 

9.4. CONCLUSIONS

(Mountains are created by the vertical uplift of former plains, independent of any folding of the rocks underneath. The age of mountains should therefore refer to the age of vertical uplift after planation, not to the last period of folding (if the underlying bedrock happens to be folded). Most uplift occurred in the Plio-Pleistocene, or the very Late Miocene. The Neotectonic Period is demonstrated by the large amount of work listed in table 9.I. Plate tectonics, the ruling theory of the past forty years, has no adequate explanation for the widespread planation in mountain regions, or the remarkably young uplift. Indeed it is based on an association of folding and uplift that is demonstrably untrue. Plate tectonics has no plausible explanation for mountains on passive margins or continental interiors. From now on it is incumbent on those who propose models of mountain formation to do two things: Incorporate planation surfaces into the story (or prove there was no former planation). – Either disprove the Neotectonic Period hypothesis, or show how their proposed mechanisms fit into the time scale of just a few million years). . . . .(Uplift occurred over a relatively short and distinct time.

 

Some unknown process created mountains after a period with little or no significant uplift. This is a deviation from uniformitarianism. The mountain building period is relatively short, and not on the same time scale as granite intrusion (which takes tens of millions of years), or plate tectonics which is supposedly continuous over hundreds of millions of years. The same rapid uplift occurs in areas where hypotheses such as mantle plumes are not appropriate. We do not yet know what causes this short, sharp period of uplift, but we can exclude naive mountain-building hypotheses that are on the wrong time scale.)

 

Isn’t Iceland a good example of this same “mountain” building (compressive?) process, and wouldn’t it fit the description, of “short, sharp period of uplift,” that you’re asking about? Or is that your point; that the mid-ocean ridge is controlled by some solar cycle?

 

~

Share this post


Link to post
Share on other sites

Essay, Iceland is being torn apart. There is a gaping rift in the middle of it. The land is high there because there is an abnormally large amount of volcanism at that point.

 

Studiot, I find arc's post about as clear as mud too.

 

Arc, please refrain from introducing more material into the discussion(!!!!!!). Please explain why in one post (referring to the Atlantic section) you say "You can see the high level of compression that it is subjected to" and in the next "There is currently no compression directly related to the mantle's subsidence in that diagram". What point are you trying to make!!?? How does this enhance your theory?

Share this post


Link to post
Share on other sites

Essay, Iceland is being torn apart. There is a gaping rift in the middle of it. The land is high there because there is an abnormally large amount of volcanism at that point.

 

...I find arc's post about as clear as mud too.

 

Sure, which is why I tried to ask the rhetorical question, hoping to highlight the contradiction (compressive? NOT!) in his 'muddy' assumptions.

===

 

But I enjoy this thread, since I learn lots of interesting new stuff about this amazing planet as I search for information on some of these 'arcing' perspectives.

 

...such as this on 'Recent Advances' in Tectonics [2012]:

http://www.intechopen.com/books/tectonics-recent-advances/

 

...or for some nice graphics, and a more general 'Jeopardy Level' overview:

https://www.superteachertools.net/jeopardyx/jeopardy-review-game-flash.php?gamefile=1392879386

 

~ ;)

Share this post


Link to post
Share on other sites

Good Morning, I hope the wedding went well.

 

Back to geology;

 

 

I'm sorry I find that explanation as clear as mud.

 

Perhaps you mean former compression?

Otherwise you need to account for the fact that the Atlantic floor is currently widening and cannot therefore be in compression, rather than tell us about the Himalayas whcih are not in your section.

 

I'm sorry studiot, yes it is former, but it will be back again in maybe 20 or 30 million years or so. That mid-ocean ridge is a mountain range built by the periodic application of tremendous pressures from the surrounding continental masses when the mantle subsides more than the convergent trenches can handle the volume. And anyway, none of those trenches are located where they could save the Atlantic ridge from the continents that are attached to its respective oceanic plates.

 

In post #377 I said;

And when the mantle again recedes in great measure millions of years from now the resulting increased compression will of course once again overwhelm and raise the Atlantic mid-ocean ridge.

 

 

Isn’t Iceland a good example of this same “mountain” building (compressive?) process, and wouldn’t it fit the description, of “short, sharp period of uplift,” that you’re asking about? Or is that your point; that the mid-ocean ridge is controlled by some solar cycle?

 

~

 

billiards, on 04 Feb 2015 - 07:07 AM, said:snapback.png

Essay, Iceland is being torn apart. There is a gaping rift in the middle of it. The land is high there because there is an abnormally large amount of volcanism at that point.

 

...I find arc's post about as clear as mud too.

 

Iceland appears to have a large source of magma available that can easily find its way to the surface. As if the ridge had been crushed and broken in greater proportions in that area.

 

I needed to include that info from Dr Ollier BTW. That it was referring to the Himalayas was not as important to that post as the sentences I emboldened, that mountains can form in sudden and short periods of time. This is important to the understanding of this model and any mountain building system it describes. If Ollier is correct what could produce such results?

 

When two continents collide you can get something as incredible as the Himalayas. When an oceanic plate collides with a continent you get something as incredible as the Andes. And so it would follow that two oceanic plates that were forced together under the immense pressures that raised those other mountain ranges, a boundary like that of the Mid-Atlantic Ridge would form a similar structure. And why would it be otherwise exempt from such tectonic forces? It wouldn't be. And what would cause it to happen so suddenly?

 

The Mid Ocean Ridge is considered the worlds largest mountain chain.

 

http://en.wikipedia.org/wiki/Mid-ocean_ridge

The continuous mountain range is 65,000 km (40,400 mi) long (several times longer than the Andes, the longest continental mountain range), and the total length of the oceanic ridge system is 80,000 km (49,700 mi) long.

 

These volcanic structures rise to more than 3657 meters (12,000 ft.) high and are 1931 kilometers (1,200 miles) wide.

 

 

Let me try it this way. Lets imagine we have two identical models of the Earth. Everything is the same except the Atlantic oceanic plate in one example is fractured and is subducting along the coast of N.A. while in the other model it is unchanged. In the scenario of the subducting model the mantle is slowly displacing outward and there would be a substantial reduction of shear stress on the Reelfoot rift, the extra shear force of the detached oceanic plate would not be imposed on the eastern side of the Reelfoot.

 

The ocean plate would instead pull at its subduction trench pulling it every cycle a little closer towards the ridge and as the ocean basin slowly widens the plate would impart gradually more shear forces causing the trench to slowly deepen. This is commonly seen at all subduction zones. As that plate became wider this metric would increase. The widest oceanic plate sections should then have the deepest trenches and this metric should be in proportion to plate width vs depth. The widest plate in this regard is currently the section of the Pacific plate that pulls on the Mariana trench when the mantle slowly displaces outward. What a coincidence.

 

So Essay is that a muddy asumption also? ^_^ I always thought they were called predictions of observations. ^_^

 

Then when the cycle changes and the mantle begins to slowly subside the compression that would normally be entirely directed to the Atlantic Mid-Ocean Ridge would be instead directed into the trench. And so the model that has a pressure relieving mechanism in the form of a convergent boundary also has a ridge with lower elevations, like the Pacific does. And as we can see a plate without a convergent boundary trench like the Atlantic, exhibits the evidence of extreme compression building up in the plate to the point that the boundary ruptures vertically, relieving the compression.

 

Something that is interesting is when mountains form in continental interiors they have a rather distinct vertical incline structure similar to the Atlantic ridge.

 

Picture below was taken by Jesse Varner and was modified by Aza Toth both of whom have no connection with this author or this paper.

post-88603-0-95950500-1423117228_thumb.jpg

The Flatirons Mountains of the North American Cordillera (Rocky Mountains) outside of Boulder Colorado shows the results of being tension fractured by large scale extension (expansion), then contracted over compressed and folded lithosphere. These structures were eroded out over 50 + million years. They must have been really something to look at when they were at their highest.

Edited by arc

Share this post


Link to post
Share on other sites

Arc,

 

I see you completely ignored my request to explain the apparent contradiction in your stance. Shall I take that to mean that your position is indefensible?

 

The seafloor bathymetry is well explained, e.g. by the model of Parsons and Sclater (1977). Basically, it is higher up at the cenntre because the material is hotter and less dense. The model also fits gravity and heatflow data. So how does your model, which has not been shown to fit any data, improve on this?

 

Additionally, the faulting on the seafloor is dominated by normal faults, try googling "abyssal hill bounding faults" if you don't believe me. These faults are ONLY formed by extension. So where is the geological evidence for compression? There is none, so how can your model fit this?

Share this post


Link to post
Share on other sites

When two continents collide you can get something as incredible as the Himalayas. When an oceanic plate collides with a continent you get something as incredible as the Andes. And so it would follow that two oceanic plates that were forced together under the immense pressures that raised those other mountain ranges, a boundary like that of the Mid-Atlantic Ridge would form a similar structure.

An example of erroneous extrapolation. There are plenty of examples where oceanic plates collide. Off the top of my head we have the Caribbean, Aleutian, Izu-Bonin-Mariana, South Sandwich, ... In these locations you get one (usually the older) plate subducting beneath the other (sometimes there is a respectable strike-slip component). The standout feature is the presence of a volcanic arc. Ironically, if arc knew a bit more about his own username perhaps he wouldn't have blundered this one so horrendously.

 

And why would it be otherwise exempt from such tectonic forces? It wouldn't be. And what would cause it to happen so suddenly?

This is a house of cards and a red herring.

Edited by billiards

Share this post


Link to post
Share on other sites

Arc,

 

I see you completely ignored my request to explain the apparent contradiction in your stance. Shall I take that to mean that your position is indefensible?

 

The seafloor bathymetry is well explained, e.g. by the model of Parsons and Sclater (1977). Basically, it is higher up at the cenntre because the material is hotter and less dense. The model also fits gravity and heatflow data. So how does your model, which has not been shown to fit any data, improve on this?

 

Additionally, the faulting on the seafloor is dominated by normal faults, try googling "abyssal hill bounding faults" if you don't believe me. These faults are ONLY formed by extension. So where is the geological evidence for compression? There is none, so how can your model fit this?

 

 

An example of erroneous extrapolation. There are plenty of examples where oceanic plates collide. Off the top of my head we have the Caribbean, Aleutian, Izu-Bonin-Mariana, South Sandwich, ... In these locations you get one (usually the older) plate subducting beneath the other (sometimes there is a respectable strike-slip component). The standout feature is the presence of a volcanic arc. Ironically, if arc knew a bit more about his own username perhaps he wouldn't have blundered this one so horrendously.

This is a house of cards and a red herring.

Bold mine.

 

You are confused again. Those are all boundaries that can easily move when the plate matrix becomes periodically loaded with the higher energy levels like those that were ascribed by Dr. Ollier for the Himalayas, energy levels not considered in the current standard model, energy levels that would easily overwhelm boundaries that will move when an increase of force is applied to them. Boundaries like the ones you mention above.

 

No, the boundaries I’m referring to are boundaries that due to their characteristics cannot move laterally or subduct beyond their current rates if an increase of energy were to be applied to them.

 

These are boundaries like the Himalayas and any other divergent boundaries that have no convergent boundary subduction trenches like those of the Pacific, as is currently the situation with the Atlantic. So if energies like those imposed on the Himalayas were to be imposed on them they would vertically rupture.

 

I’ve posted this many times and it explains as to why there is evidence of past episodes of compression in the entire plate matrix including that cross section of the Atlantic Mid-Ocean Ridge.

 

 

ANNALS OF GEOPHYSICS, SUPPLEMENT TO VOL. 49, N. 1, 2006

Mountain uplift and the Neotectonic Period

CLIFF D. OLLIER

School of Earth and Geographical Sciences, University of Western Australia, Perth, Australia

9.2. EXAMPLES

9.2.1. Tibet, Himalayas, Kunlun Mountains

(As an example, consider the timing of uplift in Tibet and its bordering mountains. Gansser (1991) wrote: «... we must realize that the morphogenic phase is not only restricted to the Himalayas but involves the whole Tibetan block. This surprising fact shows that an area of 2500000 km2 has been uplifted 3000-4000 m during Pleistocene time and that this uplift is still going on.» In places the uplift rate is 4.5 mm/yr (five times the maximum in the European Alps). According to Wu et al. (2001) from the Pliocene to the Early Quaternary (5-1.1 Million years) the Kunlun Pass area of the Tibetan Plateau was no more than 1500 m high and was warm and humid. They write: «The extreme geomorphic changes in the Kunlun Pass area reflect an abrupt uplift of the Tibet Plateau during the Early and Middle Pleistocene. The Kunlun-Yellow River tectonic movement occurred 1.1-0.6 Million years.» Zheng et al. (2000) concluded from sediments at the foot of the Kunlun Mountains that uplift began around 4.5 Million years.)

 

9.4. CONCLUSIONS

(Mountains are created by the vertical uplift of former plains, independent of any folding of the rocks underneath. The age of mountains should therefore refer to the age of vertical uplift after planation, not to the last period of folding (if the underlying bedrock happens to be folded). Most uplift occurred in the Plio-Pleistocene, or the very Late Miocene. The Neotectonic Period is demonstrated by the large amount of work listed in table 9.I. Plate tectonics, the ruling theory of the past forty years, has no adequate explanation for the widespread planation in mountain regions, or the remarkably young uplift. . . . .

. . .– Either disprove the Neotectonic Period hypothesis, or show how their proposed mechanisms fit into the time scale of just a few million years). . . . .(Uplift occurred over a relatively short and distinct time. Some unknown process created mountains after a period with little or no significant uplift. This is a deviation from uniformitarianism. The mountain building period is relatively short, and not on the same time scale as granite intrusion (which takes tens of millions of years), or plate tectonics which is supposedly continuous over hundreds of millions of years. The same rapid uplift occurs in areas where hypotheses such as mantle plumes are not appropriate. We do not yet know what causes this short, sharp period of uplift, but we can exclude naive mountain-building hypotheses that are on the wrong time scale.)

On this basis, a table of time of uplift of mountains and plateaus from around the world (table 9.I) shows a preponderance of uplift in the last few million years. This uplift of mountains appears to be a global phenomenon. It affects so-called Alpine mountains, mountains on passive continental margins, and those in deep continental interiors. The period of uplift is known as the Neotectonic Period (Morner, 1993; Ollier and Pain, 2000, 2001).

 

OK, let’s tighten this up with some more substantiation;

http://ceas.iisc.ern...h_geology06.pdf

 

Gravitational potential energy of the Tibetan Plateau and the forces driving the Indian plate

Attreyee Ghosh, William E. Holt

 

Department of Geosciences, State University of New York, Stony Brook, New York 11790, USA

Lucy M. Flesch*, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA

A. John Haines†, Bullard Laboratories, University of Cambridge, Cambridge CB3 0EZ, UK

 

ABSTRACT

"We present a study of the vertically integrated deviatoric stress field for the Indian plate and the Tibetan Plateau associated with gravitational potential energy (GPE) differences. Although the driving forces for the Indian plate have been attributed solely to the mid-oceanic ridges that surround the entire southern boundary of the plate, previous estimates of vertically integrated stress magnitudes of 6–7 1012 N/m in Tibet far exceed those of 3 1012 N/m associated with GPE at mid-oceanic ridges, calling for an additional force to satisfy the stress magnitudes in Tibet. We use the Crust 2.0 data set to infer gravitational potential energy differences in the lithosphere. We then apply the thin sheet approach in order to obtain a global solution of vertically integrated deviatoric stresses associated only with GPE differences. Our results show large N-S extensional deviatoric stresses in Tibet that the ridge-push force fails to cancel."

 

. . . ."there is no complete dynamic explanation for this large GPE of the Tibetan Plateau and the relatively fast movement of the Indian plate.

 

There is no apparent down going slab attached to the Indian plate that might assist in driving the plate into Eurasia through the slab pull mechanism" . . . . .

 

. . . . "However, the ridge push, or vertically integrated deviatoric stress magnitude, which is 3 1012 N/m (Richardson, 1992; Harper, 1975; Lister; 1975; Parsons and Richter, 1980), is not sufficient to satisfy inferred stress magnitudes of 6–7 1012 N/m that result from GPE differences between the Tibetan Plateau and the surrounding lowlands (Molnar and Lyon-Caen, 1988). An additional force is required to explain the disparity between the excess GPE of Tibet relative to that of the mid-oceanic ridges" . . . .

 

. . . ."Lithospheric density variations associated with the support of the high topography of the Tibetan Plateau give rise to lithospheric body forces and hence stresses. Although the sources of stress that drive plate motions have been ascribed to many parameters (Forsyth and Uyeda, 1975), from the point of view of stress continuity and force balance, the stresses that drive lithospheric motion arise from two sources: (1) gravity acting on density variations within the lithospheric shell on Earth, and (2) gravity acting on density variations deeper than the lithospheric shell. The latter gives rise to tractions (radial and tangential) that act on the base of the lithosphere, affecting the stress field of the lithosphere and producing dynamic topography. The former involves density variations associated with support of nondynamic components of topography".

 

Conclusions;

. . "It is clear that something is missing as a driving force that does not have its source within the lithospheric shell."

 

Well, that is impressive. Now if I were to produce evidence from other geographic areas that a similarly large scale deployment of compressive energy not only occurred in a narrow period of time, say 10 MY, but at a the same time starting 10MYA, it would mark this phenomena as a global scale event rather than one that a proponent of convection would ascribe to be a local mantle upwelling . . . .

 

http://www.scienceforums.net/topic/73730-plate-tectonic-mechanism/page-18#entry845119

 

studio Posted 3 January 2015 - 03:37 PM

“I do not know if the Earth pulsates over a long time period or not, so I am genuinely trying to help you make your model work.”

 

http://www.rochester.edu/newscenter/taking-the-pulse-of-mountain-formation-in-the-andes/

 

“This study provides increasing evidence that the plateau formed through periodic rapid pulses, not through a continuous, gradual uplift of the surface, as was traditionally thought,” said Garzione. “In geologic terms, rapid means rising one kilometer or more over several millions of years, which is very impressive.”

 

“What we are learning is that the Altiplano plateau formed by pulses of rapid surface uplift over several million years, separated by long periods (several tens of million years) of stable elevations,” said Garzione.

 

 

http://www.rochester.edu/news/show.php?id=3167

 

“Tectonic Theory May Need Revision in Light of New Study in Science”

“Mountains may experience a "growth spurt" that can double their heights in as little as two to four million years—several times faster than the prevailing tectonic theory suggests.”

 

“By studying sedimentary basins in the high Andes Mountains, the team could determine when and at what altitude these ancient sediments were deposited. That record of altitude changes shows that the Andes Mountains rose slowly for tens of millions of years, but then suddenly lifted much faster between 10 and 6 million years ago.

 

http://news.ufl.edu/archive/2008/06/andes-mountains-grew-in-rapid-spurts-not-slowly-uf-researcher-says.html

 

To reconstruct the Altiplano’s sequential rise, the researchers coaxed geochemical clues in the form of oxygen isotopes from ancient soil nodules made of calcium carbonate. The nodules were sampled from layered soil deposits between 5 million and 28 million years old.

 

Stunning isn't it. The two youngest and largest ranges by way of their own metrics occurred simultaneously. Here we have not one but two examples of massive energy dispositions in a geologic blink of an eye in opposite hemispheres at the same time. And the standard model would prescribe two different causes no doubt despite the rather devastating evidence regarding the conclusion earlier;

 

http://pubs.usgs.gov/gip/dynamic/himalaya.html

 

"It is clear that something is missing as a driving force that does not have its source within the lithospheric shell."

 

This model has from its beginning clearly predicted the observations stated above;

http://www.scienceforums.net/topic/73730-plate-tectonic-mechanism/#entry735438

 

This was post #4 of this thread.

The outer core thermal cycle is variable throughout its cycle, even from one maximum to the next in both timing and duration. Now let’s say we have an extra-long thermal expansion cycle and the divergent plate boundaries build up a very large infill, one of those that only happens every 20 or 30 million years. When the outer core begins to cool and initiates the plate’s subduction the trenches will be, like before, slower to receive the plate material than the mantles withdraw.

 

The compression begins building on the plates, being only able to overcome the trenches rates of resistances to a point. As the mantle continues down the plates are subjected to loads that require vertical movement of rock strata to relieve to massive compression building on the plates, this compression is in proportion to the length of time and degree of expansion in the previous cycle in relation to the degree of cooling in this cycle.

 

Well, you can see the evidence of a global mountain building period in two of the boundaries I had outlined previously, the Himalayan and the Andean. What do you think those two Atlantic oceanic plate sections were doing when this compression was unloading into the crust as the mantle subsided?

 

The trenches at the Pacific’s margins processed as much as they could handle. Any additional compression above and beyond those trenches ability to process it would require the vertical displacement of even highly symmetrical boundaries like the Atlantic’s to relieve the remaining energy. You can see how the Atlantic oceanic plate’s divergent boundary suffered for not having any convergent trenches along its continental margins to release the gradually increasing compression into.

 

“What we are learning is that the Altiplano plateau formed by pulses of rapid surface uplift over several million years, separated by long periods (several tens of million years) of stable elevations,”

 

The Atlantic Mid-Ocean Ridge succumbed to the compressive energy contained in the entire crust. The mantle had been slowly displacing outward during the preceding (several tens of million years), and in doing so put into place in all the world's divergent boundaries the material that would later provide the leverage that could convert that (several tens of million years) of divergent boundary infill into the gravitational potential energy capable of simultaneously raising the Himalayan and Andean ranges and rupturing the Atlantic oceanic divergent boundary. Its direct connection to its opposing and now compressing continents gave it no option other than vertical rupture to relieve the compounding energy it was subjected to.

 

That boundary was crushed between four massive continents; North America and Eurasia, and South America and Africa when the mantle subsided.

Edited by arc

Share this post


Link to post
Share on other sites

Two numbers, arc.

 

That is all that is that is needed to answer Billiard's question in post#378 fully and completely.

 

Billiards asked you to identify the location of compression on your graph and you have yet to do this some 10 posts later, despite a great deal of typing.

Since your graph has scaled axes two numbers will suffice.

 

We cannot discuss the reasons until we understand what you are claiming is (or was) in compression so all the other typing was an unfortunate waste of effort.

Edited by studiot

Share this post


Link to post
Share on other sites

 

You are confused again.

Good start. Put me in my place.

 

...

 

These are boundaries like the Himalayas and any other divergent boundaries ...

The Himalaya is not a divergent boundary. Now who's confused?

 

I’ve posted this many times and it explains as to why there is evidence of past episodes of compression in the entire plate matrix including that cross section of the Atlantic Mid-Ocean Ridge.

There is no EVIDENCE of past episodes of compression in the Atlantic Mid-Ocean Ridge in what you present. What you present is a red herring related to episodic mountain bulding. The rest of your argument is a house of cards, built on the shakey foundations of your imagination.

 

I think I just heard a pot crack.

Share this post


Link to post
Share on other sites

Two numbers, arc.

 

That is all that is that is needed to answer Billiard's question in post#378 fully and completely.

 

Billiards asked you to identify the location of compression on your graph and you have yet to do this some 10 posts later, despite a great deal of typing.

Since your graph has scaled axes two numbers will suffice.

 

We cannot discuss the reasons until we understand what you are claiming is (or was) in compression so all the other typing was an unfortunate waste of effort.

 

I'm sorry I'm such a pain in the ass. Is this what you are after?

 

post-88603-0-99765500-1423796650_thumb.jpg

 

 

There is no EVIDENCE of past episodes of compression in the Atlantic Mid-Ocean Ridge in what you present. What you present is a red herring related to episodic mountain bulding. The rest of your argument is a house of cards, built on the shakey foundations of your imagination.

 

OK, well that doesn't surprise me you would say that.

Share this post


Link to post
Share on other sites

Yes, I thought that was what you meant. Thanks, it helps to be clear.

 

This seafloor profile has nothing to do with compression. It is due to buoyancy. The science on this is pretty solid. You can read about it here: http://www2.ocean.washington.edu/oc540/lec01-3/

 

OK, well that doesn't surprise me you would say that.

You have shown no evidence for Atlantic compression (past or present). It doesn't surprise you because you agree with me?

Share this post


Link to post
Share on other sites

...now that I look at this, my question may be moot, since there aren't that many "flat" places in the Atlantic profile ...at least for this cross section; and....

 

I know the Mid-Atlantic Ridge (MAR) has varied in volume, which has contributed to sea-level change over the past hundred million years, roughly; but….

 

What I wonder about is the relatively flat parts of the ocean floor, between the mountainous spreading center and the continental slopes. All of that flat ocean floor was at one time or another, at the spreading center; and I wonder if it was mountainous then, and has since subsided, or whether the spreading was much flatter in the past. My first thought was the former, but now I’m thinking the latter.

 

AtlanticSFS-PBSmCol.gif

 

The Pacific seems to have spread faster, for a given period, and (hence?) flatter than the Atlantic.

 

It may not be "compressive" forces creating the MAR; but the MAR does seem to be spreading, or pushing, against some varying resistance.

~

 

edit: "moot" since the ocean floor may not be that flat, and/or may be buried under sediments.

Edited by Essay

Share this post


Link to post
Share on other sites

I think the max compression is at 2,000 and 4,500.

Bobbity, perhaps it is not clear but when talking about compression we are really talking about lateral compression or crustal shortening: the type of thing arc would need when the radius of the earth shrinks. When I say where is the compression, really I mean: where is the compression accommodated? Normally the compression is accommodated in some kind of mountain belt, which is why arc points to it at the middle.

 

 

...now that I look at this, my question may be moot, since there aren't that many "flat" places in the Atlantic profile ...at least for this cross section; and....

Not a moot question at all....

 

 

What I wonder about is the relatively flat parts of the ocean floor, between the mountainous spreading center and the continental slopes. All of that flat ocean floor was at one time or another, at the spreading center; and I wonder if it was mountainous then, and has since subsided, or whether the spreading was much flatter in the past. My first thought was the former, but now I’m thinking the latter.

It would have been mountains before and has since subsided. If you want to understand why I recommend studying the link I provided a few posts back: http://www2.ocean.washington.edu/oc540/lec01-3/. Of course to really understand it I would recommend reading the classic paper of Parsons and Sclater (1977) and many of the more recent follow-up papers which add new data and make incremental improvements to the model.

 

I'll take a stab at explaining it here without the maths (the maths can be found by following the links I gave earlier). When new ocean lithosphere is formed it is initially very hot and buoyant and this gives it elevated topography forming a mountain crest at the spreading centre. As the material ages it cools, undergoes thermal contraction, gets dense and lies lower, creating the flanks of the mountain. This simple thermal model of the ocean floor bathymetry fits the data remarkably well, and also fits heat flow and gravity data.

 

EDIT: simply no need for arc's compressive (shortening) regime.

EDIT2: also the faults on the ocean floor clearly show extension (yay for structural geology) so case closed.

Edited by billiards

Share this post


Link to post
Share on other sites

Bobbity, perhaps it is not clear but when talking about compression we are really talking about lateral compression or crustal shortening: the type of thing arc would need when the radius of the earth shrinks. When I say where is the compression, really I mean: where is the compression accommodated? Normally the compression is accommodated in some kind of mountain belt, which is why arc points to it at the middle. ...

I just think thousands of km of ocean floor, sloping down will result in compression at the bottom of the incline.

Share this post


Link to post
Share on other sites

That original Atlantic cross section is rather distorted. It was taken approximately where the red line below is located.

 

Images below were furnished through and in no way endorsed by http://www.geomapapp.org using GlobalMulti-Resolution Topography (GMRT) Synthesis,
Ryan, W. B. F., S.M. Carbotte, J. Coplan, S. O'Hara, A. Melkonian, R. Arko, R.A. Weissel, V. Ferrini, A. Goodwillie, F. Nitsche, J. Bonczkowski, and R. Zemsky (2009), Global Multi-Resolution Topography (GMRT) synthesis data set, Geochem. Geophys. Geosyst., 10, Q03014, doi:10.1029/2008GC002332.

post-88603-0-58759700-1423949112_thumb.png

 

As you can see the cross section data was greatly compacted laterally. I used the highest definition possible for these images and then had to crop them so they would download to this site.

 

As you can also see the rift or divergent center has a basin developing between the two opposing ridges. This proto-basin with the divergent boundary at its center maintains this configuration consistently along the entire Mid-Atlantic Ridge mountain range.

 

These are a series of images of the same location at gradually increasing definition.

 

post-88603-0-57546600-1423947265_thumb.png

 

post-88603-0-81538900-1423954594_thumb.png

 

post-88603-0-96246700-1423954609_thumb.png

 

post-88603-0-72598500-1423947298_thumb.png

 

post-88603-0-89559200-1423947322_thumb.png

 

Below are some additional cross sections along the ridge shown above. And take into consideration that their data has also been laterally compacted and the actual basin that is developing between the ridges is much wider than shown. For example in the image below the ridge on the right is over 2 km high while the basin between the ridge is around 9 km wide. The basin therefor would need to be shown as being more than 4 times wider to be in proper scale to the ridge elevation. We can clearly see now that there is two halves to a once single Atlantic ridge.

 

post-88603-0-94663200-1423947375_thumb.png

 

post-88603-0-26861800-1423947360_thumb.png

 

The distance between the ridges averages around 50km +/- 10km or so. Taking the given rate of ridge movement from;

 

http://pubs.usgs.gov/gip/dynamic/understanding.html

 

"The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr), or 25 km in a million years."

 

It would then seem correct that if the geologic clock were to be ran backwards, and the last 2 million years of divergent boundary infill was removed, we would be observing a combination of the two ridges into one structure substantially higher than the current and very low basin that now occupies the area where the actual boundary is currently separating.

 

ANNALS OF GEOPHYSICS, SUPPLEMENT TO VOL. 49, N. 1, 2006
Mountain uplift and the Neotectonic Period
CLIFF D. OLLIER
School of Earth and Geographical Sciences, University of Western Australia, Perth, Australia

 

According to Wu et al. (2001) from the Pliocene to the Early Quaternary (5-1.1 Million years) the Kunlun Pass area of the Tibetan Plateau was no more than 1500 m high and was warm and humid. They write: «The extreme geomorphic changes in the Kunlun Pass area reflect an abrupt uplift of the Tibet Plateau during the Early and Middle Pleistocene. The Kunlun-Yellow River tectonic movement occurred 1.1-0.6 Million years.» Zheng et al. (2000) concluded from sediments at the foot of the Kunlun Mountains that uplift began around 4.5 Million years.)

 

So this would put that massive pressure ridge that we call the Atlantic Mid-Ocean Ridge in the right timeline. Since that global period of mountain building ended there has been many much smaller and more typical periods of crustal compression that merely favors subduction.

 

The mountain building periods require prior extended periods of almost continual outward mantle displacement to put in place an unusually large inventory of divergent boundary material. This material is what provided the higher level of gravitational potential energy derived compression when the mantle eventually subsided. The period in question would be when the Basin and Range Province was created along with many other documented cases of crustal extension that took place in the Miocene.

 

http://en.wikipedia.org/wiki/Basin_and_Range_Province

"Opinions vary regarding the total extension of the region, however the median estimate is about 100% total lateral extension. Total lateral displacement in the Basin and Range varies from 60 – 300 km since the onset of extension in the Early Miocene with the southern portion of the province representing a greater degree of displacement than the north."

 

The Miocene Epoch was 23.03 to 5.3 million years ago. The earth went from the Oligocene Epoch through the Miocene and into the Pliocene. The Pliocene was followed by the Pleistocene, 2.6 million to 11,700 years ago. The Plio-Pleistocene mountain building period would correctly fall into place when the two now separated halves of the Atlantic ridge were formed by compression as a single, if only temporary, mountain ridge.

Edited by arc

Share this post


Link to post
Share on other sites

A recent discovery down under has bearing on this.

 

https://twitter.com/eurogeosciences/status/563786008823472128

This is deserving of its own thread:

 

see also:

 

New Scientist article:

http://www.newscientist.com/article/mg22530074.700-mini-earthquakes-reveal-lubricant-for-tectonic-plates.html?utm_source=NSNS&utm_medium=SOC&utm_campaign=twitter&cmpid=SOC|NSNS|2014-GLOBAL-twitter#.VNObqC7p-a5

 

Nature News and Views:

http://www.nature.com/nature/journal/v518/n7537/full/518039a.html#ref12

 

The Nature Letter proper:

http://www.nature.com/nature/journal/v518/n7537/full/nature14146.html

 

I have done some of my own research looking at the anisotropy in the subslab asthenospheric mantle and have found independent evidence that the slab is decoupled from the asthenosphere. Therefore, the existence of this thin decoupling channel is extremely interesting and provides a plausible mechanism for me to explain my results. It also means that the geodynamics community will seriously have to reevaluate the way they model subduction.

That original Atlantic cross section is rather distorted. It was taken approximately where the red line below is located....

Yes, there is a rift in the middle of the ridge. That is an extensional feature because the two halfs of the plate are drifting apart. I think we agree on that.

 

However, your attempting to fit this into the context of your model is reminiscent of a child attempting to force a square peg through a round hole.

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.