Bicycle Mechanics - bad chain?

check this out-brand new trek madone 5.5. shifting into big 'ring yesterday, chain overshoots, goes slack, then taut, grind, crunch, snap! damage report: broken chain, horribly {!!!!!** gouged dura ace crank arm, superficial seat and chain stay damage, rear wheel out of true due to one spoke showing deformity from its interaction with the flailing chain. needless to say, i'm heartbroken over the cosmetic damage to my new bike!!!! but i'm stunned at what just happened. i have never had this happen despite throwing chains
who-knows-how-many-times in my 25 years of cycling!!! upon closer inspection, i discover that the link that broke in the chain was not labeled shimano like the rest of the chain, but says KMC and appears to be some sort of removable link with a figure-8 style hole instead of the single hole where the rivit goes thru. anyone got any thoughts here??

Uh yeah, that would be the masterlink. And it's hard to tell exactly what happened from your post. I'm guessin the chain got stuck between the big ring in the rear and the spokes?

If so that's a derailleur limit adjustment problem, the chain breaking was just a consequence of it going into the back wheel.

are these masterlonks problematic? anytime i've purchased a chain with one, i've not used it-questioning its strength. my trek dealer says the bikes are not supposed to come with them any longer because they were "popping" off. any negative experience with them?

Its sounds to me like when you overshifted, the chain got jammed in between the chainring and the crank arm, and the continued force from pedaling broke the removable link. You must have really been cranking on it to break the link. The KMC is the weak link, so to speak, so thats why it broke.

Doesn't sound like a chain failure caused your problem, overshifting is what caused the problem and thats due to either operator error or misadjuster front der. If the chain hadn't broken, you would have torn off your rear der and probably had the same result.