What is the impact of divergent tectonic plates on old mountain ranges?
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 where you have the same thing. Precambrian mountain ranges overlain by Cretaceous sediments (folded into mountain ranges) are being torn apart to form the Dead Sea depression.