"It's still a bit of a shock I got in the squad and [as for] starting this weekend - I can't wait. [My ambitions at the start of the season] were just to break into the Blues squad," Allen told BBC Wales.
Sam Warburton: Cory Allen born for big time - Warburton
Prop Jones made his international debut against the Barbarians in 2012 and came on as a replacement in the 22-18 win over Japan in June.
"We have made a number of changes due to injury, but it's a great opportunity for players we have been very impressed with," added Gatland.
"For Cory it will be his first taste of international rugby and for Rhodri [Jones] a chance to gain more experience.
"Justin [Tipuric] played very well off the bench last weekend and Dan's injury gives him the chance to start the game."
Gatland also paid tribute to prop Gethin Jenkins.
The British and Irish Lions loose-head, who made his debut against Romania in 2002, joins Gareth Thomas, Stephen Jones and Martyn Williams as players with a century of caps for Wales.
"Saturday will be a huge occasion for Gethin and a fantastic milestone," said the Wales coach.
Team to face Argentina
Leigh Halfpenny (Blues); George North (Northampton Saints), Cory Allen (Blues), Scott Williams (Scarlets), Liam Williams (Scarlets); Dan Biggar (Ospreys), Mike Phillips (unattached); Gethin Jenkins (Blues), Richard Hibbard (Ospreys), Rhodri Jones (Scarlets), Bradley Davies (Blues), Alun Wyn Jones (Ospreys), Sam Warburton (Blues, capt), Toby Faletau (Dragons), Justin Tipuric (Ospreys).
Ken Owens (Scarlets), Paul James (Bath), Samson Lee (Scarlets), Luke Charteris (Perpignan), Ryan Jones (Ospreys), Lloyd Williams (Blues), James Hook (Perpignan), Ashley Beck (Ospreys).
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