After taking off from Ezeiza, today at around 2330 local time, it declared an emergency and returned to the airport... anyone has any idea what happened?

Overweight landing SOP is to declare 'emergency'.

Non event other than that.

Who's SOP?

SOP = Standard Operating Procedure.

Was told it was radar system failure. The Amazon is not the place to be without a radar. RTB (Return To Base, in this case EZE) to replace radar. Flight re-dispatched.

why didnt burn fuel until on max landing weight??? I dont think a radar fault needs an overweight landing

If the dump system is inop you'd have to fly in circles for over 5-6 hrs, or longer, to get down to max landing weight. These aren't 'puddle jumpers'.

Three guys, with probably 30,000+ hrs, came to a decision that worked out fine.

Thanks for the information