It looks almost like a burn....like someone put a flame to the bark. I have never seen anything like it. If it isn't a burn, it has to be a fungus, virus, bacterial infection, insect damage or some combination of these. Without knowing more, I would begin by treating the tree with a fungicide and try to eliminate fungus as a possible cause. It shouldn't hurt the tree to try that. If that doesn't work, and you see no sign of insect infestation, you may be left with an untreatable condition that the tree will either out grow or succomb to. That's the best I can offer....hope it helps. Good luck!

How it got infected? It seems you have not taken proper care of it..there are many pesticides available in the market use them..may be the infection will go and you will get good mango

Treat it with a heavy dose of fungicide and an insecticide. Then give it a light dose of major and minor trace element fertilizer. One of the three might work. Check for boring beetles on the pruned limbs. Good luck. That's a bummer!

Also see:
http://www.quisqualis.com/egyptmanknight.html

I would do what the above said but also remove the affected growth and burn it in case it can spread. Maybe it's some form of blight. I really looks like someone took a flame to the branch already.

I had one more thought. The soil around your tree almost looks like our beach sand. Could there be a salt intrusion issue?