So Ten caused the cracks when he regenerated in the TARDIS. Its all slowly coming together...
for what its worth all signs point towards that.
Nope, Ten didn't cause the crack.
If you looked carefully, the fragment was an exact match to Eleven's new TARDIS. Also, the crack seem to be getting thicker as we get towards the series finale, so I suspect something Eleven is going to do in the future would cause the TARDIS to explode. I guess thats why the final episode is called "The Big Bang". And the crack radiates from the point of explosion into both the past and future, along the TARDIS' trajectory.