What happened? tube blew the rim? Had a puncture today, removed the tube, patched it and made it home.
Obviously since I only have a mini-pump I could not inflate it to my 8 bar usual pressure.

When home, I took the wheel upstairs to inflate it with my big pump. Inflated it to 8 bar and put the tire aside to mount it on the bike tomorrow.

A couple of minutes later: BANG and when I looked, I saw this:




Seems like the tube exploded (not exactly around the valve but not far from it: you can see the cap on the far right in the second pic) and blew off the "clich" part of the rim.

What could have caused this? the tire is a Conti 4S that can handle 8 bar, the tube is a Schwalbe standard tube that does support 700x23 dimension. The rim was a Mavic Open Pro...

Sucks,... did not feel like buying a new wheel now :(
This kind of failure is typically caused by excessive wear on the brake surface of the rim.  

Every time you apply your brakes, you are polishing small amounts of metal away from the rim. Eventually, the rim gets too thin and weak, and will crack, like you have seen in your photo, from the normal inflation pressure of the tire. 

In general, this means tht the rim has been used beyond its life. If it is a new, or lightly used rim, it may be a manufacturing defect.