I'm continuing to work on my map, and one thing that's giving me difficulty is figuring out the geology of a region that I wanted to be similar to the Ethiopian highlands and African rift valley. This area is marked dry highlands on the map below. (It's otherwise a little outdated now, but gives a solid idea for this question.)
According to wikipedia the highlands are, well, high, because magma pushed up the surface of Earth, forming a mountain range there and in the nearby Arabian peninsula. This appears to be the reason you get legendarily massive plateaus on top of tectonic plates that are separating, and creating the rift valley. (Or that and some more volcanic activity and erosion.)
My question is pretty simple: Is rising magma and separating tectonic plates adequate to create a region like the Ethiopian highlands in the area marked on the map above, or is there an important context I'm ignoring? If so, what should I do to justify it?