Moving That Much Mass Introduces Energy
The area of the Somali plate is 16.7 M square km. Assuming you were raising the plate by 1km in the space of three months, using the most conservative values you provided in comments, how much energy would be released?
1 km in 3 months is about 0.15 mm/s. (For comparison, its current velocity on the mantle is 6mm/year.) Because magic is involved, we'll assume it doesn't bind with any adjacent plates and cause world-ending earthquakes off the bat.
Assuming that more stone is being magically conjured to fill the gap created by the rising kilometre of rock, you just need to accelerate 16.7M cubic km of (for simplicity) granite to 0.15 mm/s.
This works out to energy expended ~= 5.5 * 10^15 J/s. That's a little more than a megaton of TNT equivalent... every second. For three months. 7.8 million megaton bombs. To say that this dwarfs the nuclear arsenals of the planet is to radically understate the problem.
This, again, assumes that magic is dealing with crustal collapse and other calamities. Just moving that much mass is going to introduce an enormous amount of energy into the environment. If you're already using magic, why not just have it poof the plate into its new position, removing all the matter that would be in the way? You'd murder everyone in Madagascar and the east coast of southern Africa, but it would save a lot of headaches.