I would send them both home for the week without pay. That is suspension. Note in file about altercation ... inform them that next time anything remotely happens with anyone ... that person is gone. you set precident for unemployment for dismissal with cause and you punish them for being dinks. Nothing hurts more than messing with their pay. OH, and make them write down an entire altercation report ... make them do it IN DETAIL.
Not only is that unprofessional, but anything involving physical violence is a once and done ... if it's a he said, she said ... cover your ***, get the altercation in writing, get the discipline history in writing, steps you took to resolve workplace drama and if they even get testy with each other ... you just have to say 'do I have to fire someone?'