Kashirina, conceding 28kg in bodyweight to her rival, took the initiative as she became the first woman to snatch over 150kg.
But Zhou hit back to equal the world best clean and jerk of 187kg - the only record still standing after a crunch clash - and triumph in dramatic fashion by just a single kilogram overall.
Zhou's total of 333kg breaks her own previous world best by a clear five kilos and adds the Olympic title to the world crown she claimed in Paris last November, where she also pushed four-time European champion Kashirina into second place.
Such was the dominance of the leading duo that a total of 294kg claimed bronze for Armenia's Hripsime Khurshudyan, who edged out 2008 gold medallist Jang Mi-Ran (289kg).
'I think it all stems from training and then from determination, single-minded determination,' Zhou said.
'Every athlete dreams of making it to the Olympic Games one day and then once there to become a challenger for medals and then to break world records.
'This I think is what the Olympic Games are all about.'