I don't know if it's of any significance, but the OP was running an odd-number cog on an even chainring. Jedi Master Sheldon contraindicates this, as it contributes to uneven chain wear (if I understand him correctly, which isn't certain). 48/17 is a pretty beefy ratio, especially with a 230lb guy mashing down suddenly-- could uneven chain wear combined with such a monster load have caused the cahin to fail?

I''m not asserting anything here, just asking, so I'd appreciate not being jumped on if I'm way off the mark...