Code First, Model First, or Behavior First? (Talking On Plate Tectonics, Earth Science).

Sergey D. Sukhotinsky's Blog
http://weblogs.asp.net/sergeys/archive/2011/08/30/code-first-model-first-or-behavior-first-talking-on-plate-tectonics-earth-science.aspx

Code First, Model First, or Behavior First? (Talking On Plate Tectonics, Earth Science).               

Software industry to address Plate Tectonic.
   With the "Model First" concept a developer still needs to suggest a model. What if a model were to be built automatically, based on a set of observations? That's probably too fantastic in a general case. But, does a special case exist to justify it? I think, yes, this can be Plate Tectonics, Earth Science.

   The very nature of Earth Science is that it's impossible to reach the depths of the Earth to see directly what's going on there. So different models exist to explain the tectonic processes. The most widely accepted one is Plate Tectonics. Phrases like "is thought to be", "is widely accepted", "is postulated", etc are not uncommon within the model. The mainstream of the model does not take Earth as a rotating body at all and one could find other issues with the model on the closer look at it.

   Software "Model First" evangelists are scientists, for sure. They are the most advanced specialists to handle future "Behavior First" concept. So, the question is, why have Software and related industries wait for "Earth Science" scientists to figure out which model fits better the geology/geophysics observations? Why not to help them to convert the stream of ongoing observations into the process of building the relevant model? The best professionals to handle the task belong to software industry.

   Let's name some reasons why Software and related industries may consider participating in building the relevant Tectonic model of the Earth:

a) Software industry:
   1. The industry possesses the best professionals to handle the task. The task spans both "Model First" and "Behavior First" domains. It would be only natural for the industry to jump on the train, running one of the AI rails.
   2. Good knowledge of possible future seismic events is vital to the industry.

b) Electronic Components and Electronic Devices industries:
   1. Steady supply of materials is vital for the industry. Plate Tectonics is not only about how do continents move. Plate Tectonics is also about how do the deposits of elements form and where to dig them. (See "Porphyry Copper. More On Reshaping Pangaea (Gondwana)" ( http://divergent-boundaries.blogspot.com/2011/07/porphyry-copper-more-on-reshaping.html ), some ideas were left behind the post.)
   2. The same as the point 2 for Software industry.
   3. The industries could provide the hardware that is optimized to address the task.

c) Other industries, to name a few: auto-, mil- related, etc.
   1. A set of reasons including some of those mentioned above.

Suggesting Active Boundary Plate Tectonics model.
   Probably I would not post it if I, Sergey D. Sukhotinsky, the author of this message had not developed the draft of new concept of Plate Tectonics. The concept, in my opinion, is quite promising as I found it to explain the tectonics-related observations quite nicely. The story started on 26-Apr,2011 when I posted a request to "Tectonics & structural geology discussion list" <GEO-TECTONICS@JISCMAIL.AC.UK> to review new concept of forces behind continental drift, post #5932 on 26-Apr,2011 and post #5955 on 3-May, 2011.

   The concept "Active Boundary Plate Tectonics" is based on a few suggestions. Below are some adapted excepts from my post Item #6247 24-Aug 2011 12:35 - A message on Active Boundary Plate Tectonics.<GEO-TECTONICS@JISCMAIL.AC.UK>, the post in full is at the end of this message:)

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- the suggestion that under the deformations the transition layer between crust and magma propagates in the direction of lower temperature;

- the suggestion that if the transition layer reached surface, it would build either:
a) divergent boundary if enough cooling of the surface were present (water layer over oceanic floor, say East Pacific Rise);
b) convergent boundary if the transition layer reached atmosphere (not enough cooling), I'd say - Hawaii. The upper layers of magma is getting spoiled by sediments and nearby chain of underwater volcanoes can't build the strong (divergent) boundary. (We assume the region to be under compression, not extension.)

- some other suggestions to be discussed later;
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   The derived ideas range from geographically very local to the planet-wide ideas:

- Big picture on continental formation end evolution, (my (somewhat outdated) blog post "Continental Formation And Evolution Revisited". ( http://divergent-boundaries.blogspot.com/2011/05/continental-formation-and-evolution_18.html ))

- Latest super-continent Pangaea layout. There was a post on this list #6165 (13-Jul, 2011) "Request for links to resources on alternative Pangaea layouts." The proposed layout was to place Australia, India, and NZ on the West of South America. Australia to be connected to "Atacama desert" region, India's cratons to be places on the North-West of Australia. NZ to be connected to South America below Australia. One of the evidences was the location of porphyry copper deposits, (my blog post "Porphyry Copper. More On Reshaping Pangaea (Gondwana)".( http://divergent-boundaries.blogspot.com/2011/07/porphyry-copper-more-on-reshaping.html ))

- Mountain formation. (my blog post "Formation Of Mountain Ridges by Broken Process Of Subduction" ( http://divergent-boundaries.blogspot.com/2011/05/mountain-ridges-formation-keeping-it.html )). Tibet/Himalaya formation mechanism was suggested - by the series of "broken processes of subduction".

- Intra-continental tectonic processes. Some evidences of divergent processes within continents were pointed out: - my posts "The Snake River Plain As A Divergent Boundary" ( http://divergent-boundaries.blogspot.com/2011/06/snake-river-plain-as-divergent-boundary.html ), "Diverging Processes Within Las Vegas Valley" ( http://divergent-boundaries.blogspot.com/2011/07/diverging-processes-within-las-vegas.html ), "Diverging The Southern Death Valley" ( http://divergent-boundaries.blogspot.com/2011/06/diverging-southern-death-valley.html ), "Evidences Of Diverging Processes Within Tibet Mountain System." ( http://divergent-boundaries.blogspot.com/2011/08/navigate-to-abdipasa-turkey.html ), "Ural-Putorana Diverged, Suggesting The Global Mechanism" ( http://divergent-boundaries.blogspot.com/2011/08/ural-putorana-diverged-suggesting.html ), "Evidences Of Old Diverging Process Within North Anatolian Mountains. ( http://divergent-boundaries.blogspot.com/2011/08/navigate-to-abdipasa-turkey.html )".
It was suggested that the diverging processes were behind the "Flood Basalt" events. The Snake River Plain divergent process was suggested to correlate to flood basalts on the North and on the South of the plain. The event of diverging Ural from Putorana was suggested to be one of the primary cause of Siberian Traps flood basalts (my blog post "Ural-Putorana Diverged, Suggesting The Global Mechanism" ( http://divergent-boundaries.blogspot.com/2011/08/navigate-to-abdipasa-turkey.html )).

   The most exciting for me was my work on my post "Black Sea. Some Thoughts On Its Opening And On The Origin OF The Crimean Mountains." ( http://divergent-boundaries.blogspot.com/2011/08/black-sea-some-thoughts-on-its-opening.html ) The post was about that the divergent boundary - the Shatsky Ridge separated the Crimean Mountains off the Pontic Mountains. Some evidences were discussed.
Why not "Model First" ideologist to take care of Plate Tectonics model?
Thank you,
Sergey D. Sukhotinsky.


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Item #6247 (24 Aug 2011 12:35) - A message on Active Boundary Plate Tectonics.
<GEO-TECTONICS@JISCMAIL.AC.UK>
Subject: A message on Active Boundary Plate Tectonics.
Reply-To: Tectonics & structural geology discussion list <GEO-TECTONICS@JISCMAIL.AC.UK>
Date: Wed, 24 Aug 2011 12:35:17 +0300

Dear GEO-TECTONICS list members,
On 26-Apr,2011 I posted a request to review new concept of forces behind continental drift, post #5932 on 26-Apr,2011 and post #5955 on 3-May, 2011. I would agree it would be better to prepare a work, publish it, and then to discuss it on the forum, For some reason I got no option to go the standard way. Let me to sum up what I've done since then in a short message. I am not sure I'll have an opportunity to continue the work (though I'll be trying to continue it).

The initial concept did not transform too much. As for now, the concept "Active Boundary Plate Tectonics" is based on the next suggestions.

- the suggestion that under the deformations the transition layer between crust and magma propagates in the direction of lower temperature;

- the suggestion that if the transition layer reached surface, it would build either:
a) divergent boundary if enough cooling of the surface were present (water layer over oceanic floor, say East Pacific Rise);
b) convergent boundary if the transition layer reached atmosphere (not enough cooling), I'd say - Hawaii. The upper layers of magma is getting spoiled by sediments and nearby chain of underwater volcanoes can't build the strong (divergent) boundary.
- third suggestion to be discussed later;

The derived ideas range from very local geographically to planet-wide:
- Big picture on continental formation end evolution, (my blog post "Continental Formation And Evolution Revisited".)
- Pangaea layout. There was a post on this list #6165 (13-Jul, 2011) "Request for links to resources on alternative Pangaea layouts." The proposed layout was to place Australia, India, and NZ on the West of South America. Australia to be connected to "Atacama desert" region, India's cratons to be places on the North-West of Australia. NZ to be connected to South America below Australia. One of the evidences was the location of porphyry copper deposits, (my blog post "Porphyry Copper. More On Reshaping Pangaea (Gondwana)".)

- Mountain formation. (my blog post "Formation Of Mountain Ridges by Broken Process Of Subduction"). Tibet/Himalaya formation mechanism was suggested - by the consecutive "broken processes of subduction".

- Intra-continental tectonic processes. Some evidences of divergent processes within continents were pointed out: - my posts "The Snake River Plain As A Divergent Boundary", "Diverging Processes Within Las Vegas Valley", "Diverging The Southern Death Valley", "Evidences Of Diverging Processes Within Tibet Mountain System.", "Ural-Putorana Diverged, Suggesting The Global Mechanism", "Evidences Of Old Diverging Process Within North Anatolian Mountains.".

It was suggested that the diverging processes were behind the "Flood Basalt" events. The Snake River Plain divergent process was suggested to correlate to flood basalts on the North and on the South of the plain. The event of diverging Ural from Putorana was suggested to be one of the primary cause of Siberian Traps flood basalts (my blog post "Ural-Putorana Diverged, Suggesting The Global Mechanism").

A few words in conclusion. The proposed concept of Active Boundary Plate Tectonics seems to be quite efficient concept. It could be used to explain not only intercontinental tectonic processes, but also to explain very local intra-continental tectonic processes.

Thank you.
Sergey D. Sukhotinsky.
--
PS.
The most exciting for me was my work on my post "Black Sea. Some Thoughts On Its Opening And On The Origin OF The Crimean Mountains." The post was about that the divergent boundary - the Shatsky Ridge separated the Crimean Mountains off Pontic Mountains. Some evidences were discussed:

- Matching mountains on Anatolia (Dongelce) and Crimea (Laspi) side. The rectangular mountain structures can be found only in this "bent" part of Pontic Mountains.

- Matching mountains all over the divergent mountain system (Yalta, Crimea to match Aydincik-Doganyurt, Turkey; Feodosia, Crimea to match Caylioglu, Turkey; Novorossiysk-Anapa, Russia fit Carsamba, Turkey).

The mechanism that diverged the mountain system was discussed. The origin of deep see locations around Laspi was suggested.

I posted about two dozens of posts on Plate Tectonics on my blog http://divergent-boundaries.blogspot.com. Now I've made most of the posts private, but still on-demand are available the timestamped editions of them and their drafts that are stored in the cloud.

(I think, some day the blog platform host will introduce the feature to make public the saved editions of a blog post.)

Black Sea. Some Thoughts On Its Opening And On The Origin OF The Crimean Mountains.

Laspi, Crimea.
    Have you ever been to one of the most incredible places on the Earth - Laspi, Crimea, Ukraine, the place where the mountain ridges turn from parallel to perpendicular to coastline direction, and then abruptly end up with 600+ m vertical walls? Search images with "Kokiya Kaya", "Kush Kaya", "Ilyas Kaya" to get the impression of it (try views from the sea). Can a mountain ridge be formed the way it would end up with a vertical wall on its side? Unlikely, I'd say. Rather, I'd expect some tremendous force to break the ridge, and then to diverge one part of it from another over hundreds kilometers.

The driving force of the process, Shatsky Ridge, Black Sea.
   Navigate to Black Sea. Use both bathimetric satellite map and a terrain map over the region. Probably I am not the first to suggest that it looks like the very Shatsky Ridge (Black Sea) was the source of the force that diverged "Georgia-Russia-Crimea" seaside from "North Anatolia" seaside. The Shatsky Ridge acted like oceanic divergent boundary and, probably, the crust it had spread was the type of "oceanic" thickness crust. The tracks of the diverging process on shore can be seen as far as up to East end of Pontic Mountains , - East end of Pontic Mountains and Greater Caucasus were diverged some tens kilometers here. Closer to Black sea the mountains diverged roughly over twice greater distance. And under water the divergent process was even stronger. The good temperature gradient through the boundary helped it, the stronger process - the greater distance of the diverging, - the Crimea is approx 400 km north from North Anatolia now.
 
Locating the missing diverged mountain structure. 
    The divergent ridges turned south at Laspi. To locate the matching mountains on Anatolia's side, why not to look for the mountains that face north with their broken planes. The corresponding region will be the region where North Anatolian Mountains turn south, that is Bartin Province, Turkey. Let's look at the relief structure aprox 40 km East-North-East from Bartin, near Dongelce, the mountain structure with perfect right angles if seen from top. If un-diverged, the coastline would rotate the mountain structure to face the structure planes north. The structure seems to be the only such "right angles" structure for all the North Anatolian Mountains, and it's placed right when the ridges turn from north-south to east-west direction. If we assume the Anatolian side uplifted a a few hundred meters to let the structure be that deep on-shore, than the heights of the mountains on both sides seem to be roughly equal and the conclusion could be that the Dongelce mountain structure seems to match Laspi's broken ridges quite well.

Tracking the two sides of the boundary from Laspi, Crimea to Georgia.
   Let's select a point on a Georgian side to evaluate the distances for matching locations on the divergent sides. Let it be P'arts'khanaqanevi, Georgia. The suggested matching locations could be:
- Yalta, Crimea seems to match Aydincik-Doganyurt, Turkey.
- Feodosia, Crimea seems to match Caylioglu, Turkey. Using the map in "Terrain" mode we could see how well Feodosia's line of lower mountains would flow into the Caylioglu's lower mountains.
- Novorossiysk-Anapa, Russia extended fragment of mountains seems to fit Carsamba, Turkey.
The distances from Novorossiysk and Carsamba to P'arts'khanaqanevi seem to be roughly equal, - one could try tracking the rest of the two sides.

Suggesting the mechanism that diverged the ridge.
    The conditions a divergent boundary to start developing are:
a) significant deformations within the crust;
b) access for magma from beneath of the deformed region;
c) good temperature gradient that can be achieved by presence of water layer on top of the deformed region;
    Ability to develop significant deformations could be expected along the line where two plates bumped into each other previously. In our case the plates are Anatolian and Russian plates. The accreted crust on Anatolian and Russian sides got pressed against each other to create a mountain system. But the two sides of the system still were loosely coupled with each other because the accreted pieces of crust were inclined in opposite directions for the sides. The oceanic crust is denser than the plate's one, therefore the accreted piece of crust would rather  subduct its end under the plate. For Anatolian plate the accreted crust would be inclined from North to South, for Russian plate the accreted crust would be inclined from South to North.
    The two plates met only by tops of their accreted crust. There were no pieces of crust beneath the boundary, the pieces that could add strength to the boundary and could block magma from beneath.
    On deformations magma propagated upward, and with sufficient cooling, that is, with water layer on the top, the divergent boundary  developed. The northern border of the boundary was spread as The Greater Caucasus, the southern border was spread as Pontic Mountains.

Special conditions along the divergent boundary.
    The mountain system turned left around the point "Laspi-Dongelce". The mechanism of accretion was special in the region. Pieces of the crust shifted significantly perpendicular to the course of the boundary. See the evidence of the divergent processes:
- on Anatolian side -  "Evidences Of Old Diverging Process Within North Anatolian Mountains." ( http://sukhotinsky.blogspot.com/2011/08/evidences-of-old-diverging-process.html ).
- on Crimean side the evidence of the divergent processes could be the Baidar Valley. Navigate to Laspi, Crimea. The Baidar Valley will be North-East of it over few kilometers.
     Shifted pieces of crust prevented the diverging process from developing in this corner region for the reason the shifted pieces could have blocked magma from reaching the boundary and also they could have added strength to the region against the deformations. The blocked diverging process tiered both sides together in the region, so the significant diverging force was developed to break the link between the divergent sides "Laspi-Dongelce". Probably it was this force that deformed the northern side of the boundary, the fragment rotated slightly counterclockwise, thus the Crimean southern coastline is not parallel to North Anatolian coastline now.
    The coastline rotated and Crimean southwest still continue blocking the diverging process locally. As the divergent boundary - Shatsky Ridge - moved off the Crimean coast, the developing gap between the ridge and the coastline consists of thinner crust and thinner sediment layers. That's probably why this newly spread crust is the deepest place in the sea.

Active divergent boundaries and forced divergent boundaries over the Black Sea basin.
    Two active divergent boundaries were formed - Shatsky Ridge, and the ridge "Istanbul, Turkey - Sevastopol, Ukraine". "Active" means that the diverging force was developed within the boundary.  It seems, the "Istanbul - Sevastopol" boundary later had deactivated and was moved north-west by the forced diverging process, the process at which the force did not originate within the boundary, the force to diverge the basin was applied externally. A number of such forced divergent boundaries could be identified on the sea floor between the "Istanbul - Sevastopol" divergent boundary and North Anatolia as narrow trenches on the sea floor. The "Istanbul-Sevastopol" divergent boundary moved north-west and now looks more like "Burgas-Sevastopol" divergent boundary.

Black Sea northwestern basin development, the suggestion on.
   The divergent ridge would affect the region far beyond the point the ridge turned south. In fact the deformations are not local, they are at least of Europe scale. The fact that the ridge turned south, means that no divergent boundary would go north-west,  but still, the deformations caused ruptures in the  north-west crust, the ruptures, possibly, were filled with sediments, the average level of sediments lowered below sea level and, thus, the north-western basin developed.

Azov Sea development, the suggestion on.
   The "Istanbul-Sevastopol" divergent boundary can be tracked south-west, and, possible, could affected north-east as far as Azov Sea region. The ruptures, possibly, were filled with sediments, the average level of sediments lowered below sea level and, thus, the Azov Sea developed.

Some thought in conclusion.
    The concept of active divergent boundary, that is the boundary where the diverging force is getting developed, is quite efficient concept. It could be used to explain not only intercontinental tectonic processes, but also to explain very local intra-continental tectonic processes.

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reposted from http://sukhotinsky.blogspot.com/
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Evidences Of Old Diverging Process Within North Anatolian Mountains.

    Navigate to Abdipasa, Turkey. Set the map to "Terrain" mode. The small valley on the west to Abdipasa seems to be the result of a diverging process. How had the diverging process managed to took place within the mountain system, the mountain system that is thought to be under heavy compression at that time? That's one of the points of the next post on the mechanism of Black Sea opening and the Crimean Mountains origin.
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reposted from http://sukhotinsky.blogspot.com/
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Ural-Putorana Diverged, Suggesting The Global Mechanism Behind The Event.

Looking at the bigger picture.  
   "Norilsk pizza" formation of diverged mountains is incredible (see "More On Flood Basalt, Or Siberian Traps Suggested Scenario" ( http://divergent-boundaries.blogspot.com/2011/08/more-on-flood-basalt-or-siberian-traps.html )). The crust extension mechanism scenario for Siberian Traps was suggested.
   But this time let's look at the bigger picture. Take a look at the map of Siberia by "Captain Blood" "Fil:Russland topo.png" ( http://no.wikipedia.org/wiki/Fil:Russland_topo.png ) [Accessed Aug-04, 2011]. Examine the region bordered by
- Ural Mountains;
- up over Vaygach Island;
- up and right on Novaya Zemlya;
- right and down through Taymyr Peninsula;
- down Putorana Plateau all the way to Krasnoyarsk;
- from Krasnoyarsk - left through Novosibirsk - Omsk - back to South Ural Mountains;

Ural-Putorana Diverged.
   Now, the question is, - Did Ural and Putorana diverged from each other and did Novaya Zemlya and Taymyr Peninsula diverged from them as well. I think, yes, they did. I've looked through approx a couple dozens of docs on the regional geology. Mostly they were from adsabs.harvard.edu (The Smithsonian/NASA Astrophysics Data System). You may search the site with relevant keywords to find the docs, look through them and make you opinion. This post is not to prove that the diverging took place, this post is to suggest a mechanism to drive the diverging process.

Divergent boundaries are behind the forces acting on a continent's borders.  
   Let's imagine a divergent boundary in South-North direction (at the time of Siberian Traps event) similar to the current Atlantic divergent boundary. Let the boundary point to in-between what was at the time Ural and Putorana of Siberia. Another boundary to imagine would be the one corresponding to a circle of latitude in southern hemisphere similar to current divergent boundary around Antarctic. The continent under the question is somewhere between North Pole and Equator.
   The divergent boundaries are spreading out the oceanic crust. The spread crust has two options: either to get broken into pieces and then get accreted by a continent, or to subduct under the continent. In our case we have a continent driving South on the subduction zone under its south border. The force to drive the continent is developed by the south "latitude circle" divergent boundary as it acts on the continent's north border with greater force than on its south border due to the subduction process against the continent's south border.

The continent had to brake into the two subcontinents.  
   The point is that the south "latitude circle" divergent boundary does not press evenly on the north border of the continent, because another divergent boundary (South-North) approaches the continent from North. This "longitude" divergent boundary not only itself does not press on continent's border in that north location, it also blocks "latitude circle" divergent boundary from pressing on the continent border in the location. Besides, the "longitude" divergent boundary also adds pressure on the continent's north border on the left and on the right from the location.
   Let's look at the maps. If the "longitude" divergent boundary were close to Novaya Zemlya and Taymyr Peninsula, then Novaya Zemlya and Taymyr Peninsula naturally would had been saved by the "longitude" boundary from moving south. The rest of the northern border would move south with the continent. The continent had to brake back into the two subcontinents at this point: proto-Europe and proto-Asia, so to say.
   I'd like to think the subcropping basalt fields could identify the divergent regions, see the image that follows the text "Details of the Siberian Trap deposits are evident in this map" on the web page "Sction 18. Basic Science II. Impact Cratering." ( http://rst.gsfc.nasa.gov/Sect18/Sect18_4.html ) which belongs to NASA, "Remote Sensing Tutorial" by Dr. Nicholas M. Short, Sr. ( http://rst.gsfc.nasa.gov/ ) [Accessed Aug-04, 2011].

The reasons why the subcontinents had to diverge:
- Earth's spherical geometry. In high latitudes each kilometer of the propagation to South would increment the belt's length by approx 3 km. Taymyr Peninsula is about 400 km behind the location it would reach if it followed the continent. So, the resulting one thousand km, or so gap between Ural and Putorana is not unexpected.
- The "longitude" divergent boundary itself helps the sub-continents to break apart, just because of the direction of its crust spreading.
- A divergent boundary may had formed within the spreading zone like, probably, it did in the Southern Death Valley (see "Diverging The Southern Death Valley" http://divergent-boundaries.blogspot.com/2011/06/diverging-southern-death-valley.html ). The probable horst "Confidence Hills" along the center-line might mean the divergent boundary worked against the valley borders, - the temperature vertical gradient was good as the valley was underwater. But in our Ural-Putorana case I don't see horsts, rather I see grabens in North to South direction. That could mean the diverging was caused by external forces (see 2 descriptions above).

Some thoughts in conclusion.  
   Documents, I've got through, suggest the Siberian Traps event took about one million years. That means on average 100 sm per year of crust spreading total in East-West direction just between Ural and Putorana each year on the course of a million years.
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reposted from http://sukhotinsky.blogspot.com/
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More On Flood Basalt, Or Siberian Traps Suggested Scenario.

Some Siberian Traps observation. 
   Navigate to Noril'sk using a map tool, set it to "Terrain"mode". See "Imangda Rudnaya" approx 70 km East-South-East from Noril'sk. Then, see six-point divergent star relief structure aprox 30 km East-North-East from "Imangda Rudnaya". The "pizza" of mountain ridges were cut into six pieces, and the pieces were diverged off the center approx 5 km, the space between pieces was filled with basalt. How could that happen?

Suggested scenario.
- The strong diverging process caused by Moon induced deformations (Moon was closer to Earth at the time) was mostly located on North and the continent was accreting incoming crust from North.
-The belt on Earth surface (corresponding to a circle of latitude(or parallel)) consisting of a) cratons, b) accreted chunks of oceanic crust, c) just oceanic crust was moving south under the force from North.
- In higher latitudes each kilometer of the belt's propagation to South would increment the belt's length by approx 3 km.
- 10 sm/year of the propagation in the course of a million years would increase the belt's length up to 300 km.
- Cratons and newly spread oceanic crust are not easy to get broken to compensate the expanded belt. The assembly of loosely coupled chunks of accreted crust would disassemble to accommodate the increased surface even without the help of extension force. The loosely coupled chunks would spread just because of the deformations caused by Moon and/or by the deformations caused by the incoming subducting crust.

Pangaea-related consideration.
   If the scenario is valid and the movement of East Pangaea was persistent on the course of at least 100 My, then, would not it mean that the entire Pangaea was located around South Pole before braking-up?
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reposted from http://sukhotinsky.blogspot.com/
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