The act of engaging in fellatio immediately following sodomy (commonly known as "ass to mouth"), but with the modification of the person performing the act having a mouthful of Pop Rocks. The sensation of popping candy on a penis is comparable to being sucked off by a minefield, hence the term.
"Dude, my dick feels terrible."
"What happened, think you might have caught something from that freaky broad last night?"
"No man, she gave me a Muddy Minefield."
"Dang. You should see a doctor."