Volcanic activity at Galán occurred in two separate stages, which are separated by an erosional unconformity during which the ignimbrite apron of the Toconquis group was incised by deep valleys. Mechanistically, the onset of the eruptions has been explained with delamination events during which parts of the lower crust broke off, asthenospheric material replaced the crust lost by delamination and basaltic magmas penetrated the remaining crust.