Chorizo is the central ingredient in an Argentine choripán.
A choripán is a grilled chorizo served in a crusty bread roll, often with chimichurri or salsa criolla. Its name is a combination of chori, from chorizo, and pan, meaning bread. The sandwich is widely associated with Argentina and is also popular elsewhere in South America.
Choripanes are commonly sold at roadside grills, football matches, festivals, and outdoor gatherings. The sausage is usually split or grilled whole before being placed in the bread. Chimichurri, a herb-and-vinegar sauce, is a particularly common accompaniment, although toppings vary by region and vendor.
Morcilla, or blood sausage, may appear at Argentine asados, but it is not the defining sausage of a choripán. The word choripán specifically points to the pairing of chorizo and bread, making chorizo the single canonical answer.