As we know Thor whacks away at Thanos with his weaponery. Cap whacks away with his shield. Results are mixed.

So, as in my sword thread, Scarlet Witch tries to summon help from across the dimensions. One may remember the iconic Avengers/JLA crossover with Superman yielding Mjolnir and Cap's shield.

Thus, Scarlet waves her hands and this version of Supes from the crossover appears and gets his hands on the hammer and Shield and takes on Thanos instead of Thor when Thor was whacking away at Thanos. Supes uses the weapons and the level of Kryptonian power he has. Kal is much faster and stronger than Thor, IMHO plus could heat vision Thanos in his purple face as well as pounding on him with the hammer and shield.

I will postulate that Thanos gets concussed and falls down and goes boom.