Rooney made only 17 starts in two years for Birmingham after leaving Caley Thistle in 2011 and spent last season on loan at Swindon Town, scoring 10 goals in 33 appearances, before
He has scored seven goals in 33 appearances - a third of them from the substitutes' bench - for the Latics this season.
Oldham stated on their website: "The striker had 18 months left on his contract at Boundary Park, but the mutual agreement allows him a return to Scotland with Aberdeen.
"The 25-year-old had also been a target for his former Inverness boss, Terry Butcher, now at Hibernian, but the Easter Road outfit weren't able to fund a move."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.