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.

18 May, 2011

Continental Formation And Evolution Revisited.

1. Appearance of the plates. 
   Liquid Earth cools enough to let the stuff with the highest melting temperature to solidify. The denser than magma stuff is moving down to form Earth's solid core, the less denser stuff is popping up to solidify on the surface.

2. Appearance of divergent boundaries. No subduction yet.
   The solidified stuff on the surface is getting deformed by Moon. Moon induced deformations are giving birth to the divergent boundaries ( see http://divergent-boundaries.blogspot.com/2011/05/divergent-boundaries-spreading.html ). And we assume that plates are moved by the forces that originate within the divergent boundaries. The legacy concept of asthenosphere is not used, plates now own their viscous bottom. The process of subduction is not started yet anywhere within the plates.

3. Subduction started.
   The compression between plates is getting greater and ridges over the boundaries are getting higher. At some point, most probably near Equator, a newer, therefore thinner and denser plate started subducted by older, thicker, and less denser plate. It would be natural to expect Moon to trigger the process in East-West direction, that is, the "first" subducted plate to move from East to West. The subducting plate disturbs the bottom viscous layer of the upper plate pushing the roll of viscous stuff ahead. Plates subducting from different directions are creating a lens of viscous stuff under this construct of plates.

4. Proto-cratons creation.
   The process of subduction is very intense at this point. The plates with melting temperature higher than current temperature of magma are getting semi-molten. The semi-molten stuff under the plate is getting penetrated by newer subducting plates. The newer plates have lower melting temperature. Eventually they may get molten. And trapped within the much more viscous stuff they would look like huge anomalies with higher seismic waves speed surrounded with the less molten stuff of lower seismic waves speed. The resulting thick constructs may, therefore have less dense and much more solidified bottom than its middle layer. This effectively would lead to almost absence of the so called "asthenosphere" layer on the bottom of the construct. I'd like to call the constructs proto-cratons.

5. "The Ring Of Fire" sets around the cluster of proto-cratons.
   The cluster of proto-cratons gets too thick to maintain subduction within the cluster. The Ring Of Fire - the circle of subduction sets around the cluster.

6. Two types of divergent boundaries.
   Now and on two types of divergent boundaries are spreading the solidified magma:
-  First type, divergent boundaries that move plates towards the subduction (directly or indirectly by pushing other boundaries  towards the subduction zone).
- Second type, divergent boundaries within the cluster of proto-cratons. These boundaries move deep rooted proto-cratons. And they do the job against counter-acted subduction process. Thus, boundaries of this type develop higher ridges to gain greater force than the ridges of boundaries of first type.

7. Some types of mountains.
- Type 1. A divergent boundary creates a ridge. Then the boundary deactivates for some reason, say, the plates breaks along another fault line.
- Type 2. A divergent boundary (probably deactivated at this time) reaches subduction zone. It's hard to imagine how the ridge would go under the upper plate. Rather as the ridge interior is still semi-molten, the ridge would break along its line. The loosen chunk on the continent's side would rotate and expose its sharp edge on surface. the incoming plate would again try to subduct under it. The loosen chunk after the rotation can produce high mountain as it can go as deep as hundreds kilometers.
- Other types. A convergent and other types of boundaries between plates are beyond the scope of this posting.

8. Tibet/Himalayan creation.
   So, the creation of Tibet/Himalayan would take:
- a number of divergent boundaries on the ocean floor;
- subducting the floor against the continent to create a number of high ridges;
- pressing the messed plates with the incoming continent from the other side of the floor.
- a divergent boundary moving the continent off;
- repeating from the beginning as many times as needed;
 - placing some cratons around the area to not let the subducted plates leave the region in the molten state; the locked molten stuff will be pushing the Plato even higher.


9. "The Ring Of Fire" cycle approx 300 million years. Or a time to cast away stones, and a time to gather stones together (Ecclesiastes 3:5).
   The Ring Of Fire changes its shape as the divergent boundaries within the cluster of proto-cratons expand the cluster area. When the cluster gets all the surface, The Ring Of Fire collapses. There are no place on Earth to cheaply (in terms of energy) allocate the solidified stuff produced by divergent boundaries. So, new subduction line develops. And the process repeats from the step 3 as described above.
   Let's calculate the cycle of The Ring Of Fire, that is, the cycle the continents would get cast away and then gathered together. If we assume that opposite sides of The Ring are approaching each other at 15 sm/year, we would get roughly 40000km/15sm = 40 million meters / 0.15 meter ~ approx 300 million (years).

10. Persistent location of the point of start/collapse of The Ring Of Fire between cycles.
   It was mentioned on step 3 that it would be natural to expect Moon to trigger the process of first subduction in East-West direction.  It would also be natural to expect that the initial subduction line won't be able to move from West to East due to Moon's tidal activity. Also it can't move from East to West as the subduction has already built the continent on the West of it. In other words, the point of start of The Ring Of Fire will be rather close to the point of its collapse in the sense it will be the Eastern border of the continent again. With each cycle the continent would add more ridges to its Eastern border.
   This way The Ring Of Fire with each its cycle is adding more and more ocean ridges to Tibet/Himalayan cluster, and subducting more and more stuff under/inside the cluster's body.
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reposted from http://sukhotinsky.blogspot.com/
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