Dorfs don't have parties. Beards have parties and the dorfs are just along for the ride. What a dwarven beard does to party is a mystery known only to Armok.
You have a lot of dorfs with nothing to do standing around in a very small meeting space. That's pretty much guaranteed someone is going to throw a party. Although it is impressive how many you got partying at once...
If you'd prefer they didn't faff off quite as much, and instead did whatever it is that you have them assigned to do, make a much larger meeting area. They will tend to spread out more, which makes for less socializing and less chances of parties. I usually make my meeting areas at least 30x30.
The other thing to do is keep the little buggers busy! Get them all to hauling if nothing else. Get miners mining just for stone to be hauled. Make masons build blocks on repeat. Set up smelters. Keep food and booze production going. Constantly make rock crafts. Give 'em enough stuff to do and they won't socialize as much either.
Highly-socialized dorfs aren't necessarily a bad thing -- until a couple die of natural causes. (Natural causes for a dorf include things like being pincushioned by arrows, taking a goblin spear to the face, falling off cliffs or stairs, many forms of magma, rotting from the inside out from a forgotten beast attack, drowning in a foot of water, etc, etc) If everyone is friends with everyone else, you're just asking for a tantrum spiral at the slightest provocation.
Of course, that could be something to look forward to.