The Independent Citing Commissioner Murray Whyte, of Ireland, found Galarza had been guilty of "contact with the eye or eye area" of All Black Brodie Retallick in the Wembley match.
The suspension takes effect immediately and leaves the Pumas with only three recognised locks, one of whom is injured, as they prepare to tackle Georgia on Friday in what is a must-win game if they are to have a realistic chance of progressing from Pool C to the quarter-finals.
Argentina's Juan Manuel Leguizamon was quoted by Argentine daily La Nacion as saying that the team was shocked by the severity of the punishment for Galarza.
"We didn't expect something like that," Leguizamon told the paper.
"There's not much time now (to think about it, but) we're all with the Flaco (thin one)," the flanker added of Galarza. "We can't let our minds stray (with this) because in less than two days time we have an extremely important match."
The only fit locks for Friday's game against Georgia in Gloucester are Matias Alemanno and Tomas Lavanini, while Guido Petti has been advised that he needs more time to recover from a head knock sustained against New Zealand.
Javier Ortega Desio, a back row forward, has been named on the bench as a replacement lock.
"The Judicial Officer deemed the act of foul play merited a low-end entry point of 12 weeks," organisers said in a statement announcing Galarza's ban.
An additional week was added as a deterrent against such acts, though Galarza's suspension was reduced to nine weeks after taking into account mitigating factors including his excellent disciplinary record.
As well as missing the rest of the Rugby World Cup, Galarza will be unavailable for his English club, Gloucester, until the ban ends on Nov. 26.
(Additional reporting by Rex Gowar; Editing by David Goodman)
