5

The example of the East African Rift was given in a different answer. Splitting of mountain ranges in two becomes even more apparent as you go up north from there. The Red Sea between Egypt and Saudi Arabia is a young new spreading ocean, that cuts through Precambrian mountains. Further north from there, the Dead Sea is a combined transform–rift zone ...


4

Divergent boundaries are going to form where the crust is weak and thin, a divergent boundary siis very unlikely to form in an existing mountain range. Imagine trying to pull apart a lumpy cookie, is it going to break through the thick lumps or the thin areas. That's not saying a rift could not cut across a mountain range but it will be very unlikely, it ...


2

If you want to know about what happens with diverging plates, the best example to look at is the East African Rift Valley. An existing plate is forced to split apart by a mantle plume or plumes, and this is likely to be accompanied by volcanism as is the case in East Africa. It is theoretically possible for the rift to cut through mountains, and this seems ...


2

The answers so far are broadly correct. Iceland has formed from a coincidence of a constructive plate margin and a mantle plume, or "hot spot". But to really understand why Iceland is there we need to look at a normal constructive plate boundary. A normal mid-ocean ridge is formed where two plates spread apart so that the mantle, which is at a certain ...


1

The crust is actually getting thicker very gradually as the Earth cools down. This process is well seen on Mars, where due to its smaller size and greater distance from the sun, Mars is cooling faster than the Earth. No one knows exactly how thick the Martian crust is, but what we do know is that magma can no longer find its way to the surface. All the ...


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