Box Office Mojo only seems to track the domestic (US) weekly takings. But running the numbers;
Avengers' original 9 week US run (before the re-release): $835,781,161
Avatar's 9 week US run: $428,865,132
Avengers was front-loaded. 79% of its domestic takings to this point were in the first two weeks. By the 9th week it only made $3.1 million domestically, 14th biggest taking at the box office for the week.
Avatar on the other hand kept chugging along. It made $19.5 million in its 9th week, 4th biggest taking at the box office for that week. It would remain top-10 until its 13th week in domestic cinemas.