The Dutch netted from their third corner in the 45th minute through Carlien Dirkse van den Heuvel's rebound and nine minutes later Maartje Paumen got their second to wrap up the victory.
The two sides had largely cancelled each other out in the first half but the Dutch took control after the break - leaving Argentina hardly any space to threaten.
"We saved the best for last. We were so on the ball, so aggressive. Crazy," said Naomi van As, who already won gold in Beijing.
"Maartje and me, we looked at each other during the break and I said to her 'we're going to grab it'. We dominated."
So they did in the second half. Argentina keeper Florencia Mutio saved Paumen's direct shot but had no chance with Van den Heuvel's rebound.
That set the sea of orange fans roaring and a Dutch brass band picking up their tunes before Paumen scored with a hard drag flick just below the crossbar from a penalty corner.
Paumen, who scored 11 times at the Beijing Games, has an Olympic record total of 14 goals, though the Dutch skipper had not scored in London until the semi-final against New Zealand when she grabbed two penalty corner goals that kept her side in the tournament after they trailed twice.
"I promised. I told you that the goals were coming when they matter," a beaming Paumen said, wearing her gold medal.
"Four years ago it was also an amazing feeling. It's amazing again now. Four years ago I was another player. Both are really great, but this (medal) is bigger and heavier."
Max Caldas, the Dutch coach, said the victory showed his side's global dominance.
"The girls made a commitment to be better than better," Caldas said.
"To be the best in the world is better than to be world champion. To be world champion, you do it only once and to be the best in the world you do it every day. My girls are amazing."
The Dutch victory again shattered Argentina captain Luciana Aymar's dream of achieving her first Olympic title.
But the record seven-times world player of the year, who celebrated her 35th birthday on Friday, refused to rule out that she would come back trying for Olympic gold at Rio in 2016.
Aymar, who has won every major title except Olympic gold, had said as recently as last week she would retire from international hockey.
Asked after the match about her plans, however, she said repeatedly she just did not know.
"I don't know. It's going to be extremely difficult not to find me on the pitch again."
Wrapped in an Argentine flag Aymar, who was in tears when she took the lap of honour, quickly picked herself up again as her team encircled her to celebrate the silver medal and her career.
"I decided to overcome my sadness and celebrate that we had won silver," Aymar said.
Earlier, hosts Britain beat New Zealand 3-1 to take bronze, their first Olympic medal in 20 years, winning a match played mostly in midfield in which all the goals came from set-piece penalty corners, just like in the final.
- Maartje Paumen