We experienced a spontaneous sunroof explosion. Vehicle was towed to the dealership. Sunroof is being replaced under warrenty. The vehicle is presently stored underroof at Barkley GMC, Tuscaloosa, AL. After the very loud explosion, I pulled to the side of the road and engaged On-Star for a wrecker. There were no warning lights… just a spontaneous explosion … blew out the entire sunroof.