Let me not to the marriage of true minds...

One aspect of Zabriskie point that strikes me as truly optimistic, especially in Antonioni's overall body of work, is its utopian union, however temporary, of the two main strands of counter-culture and political protest in late 60s early 70s US: the pacifist hippies and the more violent protesters, such as the Weathermen and the Black Panthers. Though it is never completely certain that Mark has indeed shot the policeman, it seems certain, especially when another policeman shows up in the desert, that he would be ready to do so. Daria refuses such tactics. But despite such divergences, the two can choose to unite.

Maybe, therefore, the final explosion corresponds to Daria's taking upon herself the violent methods of Mark, since he now cannot?

And maybe it's significant that her explosion is directed not against the police but against big business.