If you compare before and after shots of the plane
(yeah, it's a slow day here at work...)
You can see what's missing is the "pod" that makes up the leading edge of the wing. I'm going to have to go with a bird strike. Much like the shuttle Columbia which had wing damage on take off. A bird (or other object) cracked the leading edge and once the plane was at speed and altitude it gave way.
So there you go. A run of the mill airline accident. No reason to worry.