Rogers and Astaire appropriated an earlier version of the 'Fanchon and Marco Carioca dance routine' from Fanchon's same named Carioca stage show, mainly because of rehearsal issues with Fred and Ginger not having enough time to create an original. Astaire and Roger's version of the Carioca which has been modified over time, made "Flying Down To Rio" a huge success and Fred & Ginger a household name. It was hailed as the new ballroom dance, however it really never took off.
One of the main reasons the Carioca dance didn't take off was that the description of the dance steps were not included with the sheet music, which was becoming a popular process of not including them during the time. People had no clue how to do the dance except by taking dance lessons as the dance was just to difficult to pick up on their own. Also when the average public watched Fred and Ginger do the Carioca dance in the film, most couldn't see themselves doing it for fear of looking silly.
The Carioca music is basically a Samba with the foreheads touching (Carioca Samba if you will) and is patterned after another Brazilian dance called the Machichi. When dancing the Ballroom Carioca, Rumba movements and Fox-trot variations are executed as well as the Samba.