what conso said. The engine and pylon assembly is designed to come off on impact without compromising wing box/fuel tank integrity. by that I don't mean damage or leaks, but without catastrophic failure of the wing primary structure.
To my mind the first thing that needs to be ruled out as the cause of the "explosion" are the right MLG wheels and tyres, assuming the gear was still roughly somewhere between rear spar and LG beam after the aircraft stopped. They are a known explosion hazard and the fusible plugs may not have popped in time.