If it is the spot I think you are at one of the blocks has to be slightly melted to let you get up on top.
After melting the cube jump onto the platform to the left after you jump onto the crates that were in the cube. You should see two levers here. Keep the cube melted down to a point where you can still jump onto it. When you hit a lever another cube should come up. This one you just give two quick shots with the flamethrower. Now, jump onto the first cube then onto the one you gave the two quick shots to. Run to the edge of the cube and doublejump- this could get you enough height to hover to the cage.