Ok, Laurel, the short answer is: NO, you will not lose your U.S. citizenship if you voluntarily acquire Argentine citizenship. You may hold dual citizenship.
To lose your U.S. citizenship, you have to make an official renunciation (as in a signed document) in front of a U.S. consular officer and have the express intent of renouncing your U.S. citizenship.
Now in certain cases certain acts be deemed by the U.S. government as a renunciation of your citizenship but these are pretty unique specific cases. (example: announce on North Korean TV while sippng a Mai Tai with Kim Il Sung that you "renounce your citizenship".)
Applying for Argentine citizenship, or marrying and Argentine, or going to to Plaza San Martin, downing a bottle of Malbec, 10 empanadas and ripping your U.S. passport up and saying "good riddance" 3 times is not sufficient. (But I would YouTube it).
OK Steve pass the helmet so I can duck and cover the incoming board barrage!!