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Question on plate size in plate tectonics

  1. Apr 19, 2017 #1
    Question from an amateur:

    The earth's plates seem pretty large compared to the planet. This example has about 20 to 30 with about 6 seemingly making up the majority of the earth's surface.

    Is there a reason why they are so large?

    I'm writing a novel in which a planet, instead of having 20 to 30 plates, may have 100 small ones. That way, I don't have a handful of large oceans or large continents but a huge number of smaller Greenland to Hawaii sized island chains with dozens of large Mediterranean-sized seas.


    Is there some aspect of planetary tectonics that would explain why there would be more numerous but smaller plates?


  2. jcsd
  3. Apr 19, 2017 #2

    jim mcnamara

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    Consider: https://earth-planets-space.springeropen.com/articles/10.1186/s40623-016-0400-x

    I would look at it in this somewhat non-scientific analogy: If you take a system of objects, like the solar system:
    Few really large objects - Sun sized and larger
    More medium sized objects - hot Jupiter size
    Lots of much smaller objects. Earth and moon sizes
    Huge number of tiny objects: thousands of asteroids.

    During planetary formation, the tiny objects rained down onto the larger ones; they were subsumed.

    With plates on Earth powered by continental drift, tiny ones have been subsumed by subduction in the past, leaving larger ones still intact. New smaller plates form in active rift valleys from old larger ones.

    The article mentions something like this, but more from an obervational point of view.
  4. Apr 19, 2017 #3


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    nice article, Jim, thanks :)

    have to agree with that. There's no real reason why there should be a set number of a specific size.
    In a chaotic system that is forever changing over the millions of years, the size, shape and number is also going to be constantly changing

  5. Apr 25, 2017 #4
    Thanks all.
  6. May 3, 2017 #5

    jim mcnamara

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    Staff: Mentor

    @davenn - posts deleted.
  7. May 4, 2017 #6


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    Thanks Jim, I have deleted my one :)
  8. May 7, 2017 #7
    That seems to be an open question. As the continents are formed by convections inside the mantle, they should be much smaller because the size of a convection cell is limited by the deep of the fluid - in this case 3000 km. In addition the resulting shape and distribution of the continents should be more symmetric (e.g. like a honeycomb structure). For some reason the mantle doesn't behave like a homogeneous fluid. A possible reason could be an increasing viscosity in deeper layers of the mantle. In that case I would expect smaller continents on a world with a lower viscosite of the mantle compared to Earth. A side effect could be increased volcanism.
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