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 should leave Argentina and
apply for an indefinite spouse visa at this Office, unless Direccion Nacional
de Migraciones authorizes an alternative procedure.
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.