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What exactly happens at a continental-continental (cc) convergent boundary? I read myself through the web for the last few days and what I came up with is that such a boundary will start as an oceanic-continental (oc) one until the continental plates meet and then a huge falt mountain range like the Himalaja, Alps or Appalacian Mountains is formed.

At this point the sources I found gave me conflicting information. Either no subduction of the continental plate occurs or the continental plate is subducted and melts somewhere around 90 to 140 km down. Apparently rockes which where once part of the continental plate melt and resurface. I also heard that this is an area of ongoing research and it isn't fully understood what happens at cc convergent boundaries. So...

  • Does no subduction of the continental plate occur?

  • Does only a bit of subduction of the continental plate occur, as some of it is pulled down into the deep by the rest of the oceanic plate?

  • Does subduction occur at cc boundaries as on oo and oc boundaries, just slower and in a more quiet manner and cc boundaries usually don't last long enough?

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Both of the processes you describe occur; in some cases such as the Himalayas the plates are not subducted and a moving plate, in this case the Indian plate, bulldozes the continental crust ahead of it into a high mountain range. In most cases, such as the Pacific rim for example, subduction is the norm. Where there is subduction there are usually many volcanoes, and this is certainly the case on the Pacific rim. The subducted crust carries rock and water down into the hot mantle, where the friction,heat and water content tend to liquefy it,and it rises to the surface to form volcanoes. To answer your specific question, no. there is no subduction when continental crust meets continental crust, as is the case with the Indian plate meeting the Eurasian plate. Subduction occurs when sea floor spreading forces a plate underneath the lighter and more buoyant continental crust.

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    $\begingroup$ Where on the pacific rim is a continental-continental convergent boundary? $\endgroup$ – TheDyingOfLight Jul 13 at 14:51
  • $\begingroup$ I can't think of a convergent boundary of continental plates on the Pacific rim. The Pacific plate dives below the Eurasian plate in the north and the Australian plate in the west. Continental crust is lighter than the mantle and therefore floats. Oceanic plates tend to dive beneath it, so you can see why floating continental crust on the Indian plate didn't dive below the Eurasian plate, and why there are no volcanoes in the Himalayas (though there are other causes of vulcanism apart from subducted plates). $\endgroup$ – Michael Walsby Jul 13 at 15:33
  • $\begingroup$ The question was specifically about continental-continental boundaries - so while this is a good answer in other respects, might I suggest editing it to clarify that the Pacific Rim example doesn't apply to the question? Are there any continental-contental boundaries that do subduct? $\endgroup$ – Semidiurnal Simon Jul 15 at 20:22

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