GETTING MARRIED IN ARGENTINA
For marriage requirements, you should contact the Registry Office operating in the area where you are planning to get married. There are no special visas required for this purpose.
British nationals can travel as tourists without a visa, for up to 90 days that can be extended in the country only once.
If you marry in Argentina and wish to reside in the country you have the option of changing your status in Argentina at "Dirección Nacional de Migraciones"
Also, take into account that british nationals planning to reside in Argentina are normally asked to provide an original or certified copy of their full birth certificate (including names of parents), legalised by the FCO with the Apostille stamp and translated into spanish by an official argentine translator.