Yikes, sucks man.
Was this the crank arm bolt on the quarq? From switching bikes too much or something, or literally the bolt just decided to die?
FYI I threw my bike across the road one day during intervals when my tire slit open and I was in the middle of no where. I scratched my seatstay (aluminium) very similar to the main wound of your bike, I wonder if it was carbon fiber if it would have cracked!