Geodynamics of Anatolia and the Aegean sea

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Geodynamics of Anatolia and the Aegean sea

Postby Florian » Wed Jan 18, 2012 1:52 am

Understanding the geodynamics of the eastern mediterranean basin gives a lot of clues about the true nature of active margins.
In this post, I propose a multiple choice test to get familiar with the geodynamics of the Eastern Mediterranean Basin and the implications in matter of lithosphere recycling by active margins.

A lot of answers are found in this recent paper:

Le Pichon & Kreemer (2010) "The Miocene-to-Present Kinematic Evolution of the Eastern Mediterranean and Middle East and Its Implications for Dynamics" 2010 Annual Review of Earth and Planetary Sciences 38 p323-351

This figure shows the displacement of the lithosphere in the Eastern Mediterranean Basin as measured by GPS (source Jules Verne Voyager).
Each vector represents the displacement of one GPS station.

Image

The questions:

1) Is there a significant relative displacement between the GPS stations located on the coast of Lybia and Egypt, and those located in Italy/Balkans/Europe.
    a- yes
    b- no

2) What does it mean in term of convergence/divergence between Africa an Europe?
    a- Convergence
    b- Divergence
    c- no significant divergence or convergence

4) Are the displacement vectors longer or shorter in western Anatolia compared to eastern Anatolia?
    a- longer
    b- shorter

5) What does it mean in term of extension/compression inside Anatolia?
    a- extension
    b- compression

6) What is the origin of the dextral displacement along the north Anatolian transform fault
    a- A southwestward displacement of mobile Anatolian/Aegean lithosphere (and mantle) inside a static platform including the Mediterranean sea+Africa+Europe
    b- A northeastward displacement of a rigid block formed by the Mediterranean sea+Africa+Europe toward a static block including Anatolia and the Agean sea.

7) To what would you compare the motion of the lithosphere of Anatolia/Aegean sea?
    a- the rotation of a rigid plate
    b- a flowing glacier

8) Knowing that geological data indicate that Eastern Anatolia underwent a fast recent uplift, and knowing that the topography is lowering from East Anatolia to the Mediterranean sea what could be the driving force at the origin of the observed motion?
    a- Subduction of the Mediterranean Sea toward and under the Aegean Sea
    b- Gravity flow of uplifted Anatolian lithosphere

9) What will happen to the Mediterranean lithosphere if Aegean lithospheric/mantelic material is flowing over it?
    a- nothing
    b- progressively sink under the load of the flowing material

10) According to you, what terminology would give a better description of the phenomenon described in question 9)?
    a- subduction
    b- overduction

11) We've seen that the surface of the mobile lithosphere is in extension (expansion), see question 5). Considering that expanding and flowing lithosphere progressively covers Mediterranean lithosphere, how would you compare the surface of covering and covered lithosphere?
    a- covering larger than covered
    b- covering smaller than covered
    c- covering equal to covered

12) Does it correspond locally to a net surface reduction of Earth's lithosphere?
    a- yes
    b- no

13) Could it be described as a new layer of flowing material covering an older layer without any surface reduction?
    a- yes
    b- no

14) If a new layer of material is added at the surface of a sphere, what does happen to the surface of the sphere?
    a- increase
    b- decrease

15) What does happen to the sphere volume?
    a- increase
    b- decrease

I will give my answer with some comments in the next post.
If 50 million believe in a fallacy, it is still a fallacy. Sam W Carey
Florian
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Re: Geodynamics of Anatolia and the Aegean sea

Postby Florian » Sat Dec 28, 2013 1:05 pm

And now my answers!

Florian » Wed Jan 18, 2012 2:52 am wrote:1) Is there a significant relative displacement between the GPS stations located on the coast of Lybia and Egypt, and those located in Italy/Balkans/Europe.
    a- yes
    b- no


b. According to the vector length, the stations located in the hashed area do not display significant relative displacement.

2) What does it mean in term of convergence/divergence between Africa an Europe?
    a- Convergence
    b- Divergence
    c- No significant divergence or convergence


c. There is currently no significant divergence or convergence inside the hashed area. This region appears to be relatively quiet and forms a stable platform.

4) Are the displacement vectors longer or shorter in western Anatolia compared to eastern Anatolia?
    a- longer
    b- shorter


a. The vectors are growing longer toward the west.

Florian » Wed Jan 18, 2012 2:52 am wrote:5) What does it mean in term of extension/compression inside Anatolia?
    a- extension
    b- compression


It means that the lithosphere of Anatolia is under extension: the surface of lithosphere is increasing in this area.

6) What is the origin of the dextral displacement along the north Anatolian transform fault
    a- A southwestward displacement of mobile Anatolian/Aegean lithosphere (and mantle) inside a static platform including the Mediterranean sea+Africa+Europe
    b- A northeastward displacement of a rigid block formed by the Mediterranean sea+Africa+Europe toward a static block including Anatolia and the Agean sea.


a. Since Mediterranean sea+Africa+Europe form a quiet platform engulfing lithosphere in motion, well constrained within Anatolia and the Aegean Sea, interpretation a. appears to be the most logical. Accordingly, the north Anatolian transform fault marks the limit between the static lithospheric platform (north of the fault) and the mobile lithosphere (south of the fault).

7) To what would you compare the motion of the lithosphere of Anatolia/Aegean sea?
    a- the rotation of a rigid plate
    b- a flowing glacier


b. It is actually very similar to the motion of a glacier.

8) Knowing that geological data show a fast recent uplift of Eastern Anatolia, and knowing that the topography is lowering from East Anatolia to the Mediterranean sea what could be the driving force at the origin of the observed motion?
    a- Subduction of the Mediterranean Sea toward and under the Aegean Sea
    b- Gravity flow of uplifted Anatolian lithosphere/mantle


b. The westward extension of uplifted Anatolia strongly support gravity flow toward the Mediterranean Basin.

9) What will happen to the Mediterranean lithosphere if Aegean lithospheric/mantelic material is flowing over it?
    a- nothing
    b- progressively sink under the load of the flowing material


b. If the Mediterranean lithosphere gets loaded with material, the region won't be in isostatic equilibrium and the Mediterranean lithosphere will sink to compensate. This is no different than in glacial ages, when lithosphere sinks under the load of with km-thick layers of ice. One difference is that the extra load is not building rather uniformly, but progressively from one edge. As a result, the edge of the overlaid lithosphere progressively bend down, and rolls back as the mantle flow progresses and invades. This phenomenon is identical to what is described as a "subduction zone" in plate tectonics terminology.

10) According to you, what terminology would give a better description of the phenomenon described in question 9)?
    a- subduction
    b- overduction


b. It is a matter of driving force. In plate tectonics, the driving force is the sinking lithosphere, hence the term subduction. But we have seen that the real driving force is the flowing mantle and lithosphere. The lithosphere sinks because it is loaded by the mantle/lithosphere flow (let's call it tectonic flow). So overduction (by a tectonic flow) seems to be a much better terminology to describe the true nature of the phenomenon.

11) We've seen that the surface of the mobile lithosphere is in extension (expansion), see question 5). Considering that expanding and flowing lithosphere progressively covers Mediterranean lithosphere, how would you compare the surface of covering and covered lithosphere?
    a- covering larger than covered
    b- covering smaller than covered
    c- covering equal to covered


c. Logically, the surface of a covering layer of material is equal to that of the covered layer.

12) Does it correspond locally to a net surface reduction of Earth's lithosphere?
    a- yes
    b- no


b. Because the surface expansion of the covering layer compensates the surface reduction corresponding to the covered layer.

13) Could it be described as a new layer of flowing material covering an older layer without any surface reduction?
    a- yes
    b- no


a.

14) If a new layer of material is added at the surface of a sphere, what does happen to the surface of the sphere?
    a- increase
    b- decrease


a. Adding a layer to sphere, even locally, does increase the surface of the sphere.

15) What does happen to the sphere volume?
    a- increase
    b- decrease


a. Obviously.
Now, a good question is "what if the the material of the new layer comes from inside the sphere? Wouldn't that means that the volume does no change?". Yes, except if there is an input of material inside the sphere. Input that would actually be the primary cause of the output of inner material at the surface of the sphere.

In anyway, if there was no global volume change, there would be no global surface change. But here, I've shown that there is no reduction of lithosphere in a region associated to one subduction zone of the plate tectonics theory. And this can be generalized to every active margins, starting with the Scotia Sea, another region dominated by a tectonic flow very similar to the one described in this post.
So at the globe scale, active margins do not really consume lithosphere, at least not significantly enough to consume the equivalent surface produced at the Mid Ocean Ridges.
The inescapable conclusion is that the surface of Earth is increasing. Furthermore, the primary cause of that increase in surface must be an input of matter inside the planet.
If 50 million believe in a fallacy, it is still a fallacy. Sam W Carey
Florian
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Posts: 51
Joined: Sun Jul 10, 2011 9:15 am


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