My science/technology-related thoughts, sometimes controversial, sometimes can be based on limited knowledge base, logic can be non-perfect as well. I develop my vision in iterations. Don't take this blog as an attempt to convince anybody in anything.
Each post in this blog reflects my level of understanding of Tectonics of the Earth at the time the post was written; so, some posts may not necessarily be correct now.

04 August, 2011

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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