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.

16 August, 2011

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." ( ).
- 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.

reposted from

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