Thank you very much for your comments colleagues.
About the marines with their weapons after surrendering, that existed and there are many photos, one of them very famous, the manufacturer in 3D figures (which has the most complete line of figures about the Flaklands that I have ever seen), based on a line of figures on that historical photograph.
In the photo you can see an amphibious command of the Argentine Navy (the amphibious commandos as well as the marines of the amphibious operations group only acted in that operation, then they were returned to Argentina and did not fight the war).
Why did the British Marines have their rifles?
Because the group that took the islands had two clear orders 1) There should not have been British deaths. 2) The honor of the British had to be preserved.
This was because a war was not wanted, what was wanted was a negotiation in the UN.
That is why the conquest of the islands was done by so few men, some 30 professional amphibian commandos did all the work, supported from afar (far away) by a company of marines in vehicles.
The Marines were kept away because they were conscripts and they were very aggressive, it was feared that if they went into action they could kill Britons and that was not good for negotiations.
As Galtieri did not want special troops in the Malvinas (in the whole war from Argentina there were only two companies of marines, four paratroopers ina a antiareral canyon and two commando companies who were volunteers, the rest were only common infantry, this brought a lot of debate after the war, in that Argentine era had about 30,000 special troops among paratroopers, marines, mountain troops and others who did not go to the islands, nobody knows why Galtieri let the best in the continent, but it is more reoated to geopilitical tah military strategy) these commandos and marines were immediately returned to Argentina.