Lifting off

Judging by the sheer might of the guitar licks on Mastodon's latest album, "Crack the Skye," the riff god is clearly a fan. And he is not alone.

Over the course of seven years and four albums, the Atlanta quartet, which plays the House of Blues next Thursday, has steadily amassed acclaim from critics, fans, and famous admirers like Dave Grohl and Josh Homme for its brand of dense, insanely elaborate, yet often ethereal progressive metal. On the gold-selling "Skye" - the spelling and the title track are an homage to Dailor's older sister, who passed away as a teen - the band branches out even further, expanding its style palette and splitting the vocal duties among three members. (Dailor, guitarist Brent Hinds, and bassist Troy Sanders all step up to the microphone, while Bill Kelliher remains content to let his guitar sing for him.)

With passages that are just as likely to evoke Zappa and the Beach Boys as Sabbath and Slayer, "Skye" is one big zag. It's the kind of album you want to listen to over and over, lying on your bed with the headphones on, because there's so much to digest. The dramatic centerpiece - a four-part, 11-minute interlude called "The Czar," which ties into the record's not-entirely-appreciable concept about a paraplegic boy, Russian royal adviser and mystic Rasputin, and out-of-body experiences via astral projection - takes gauzy space flight on droning organs before crashing to earth in a blaze of angry metal thunder.

If all that conjures the grandiose, sometimes pretentious aspirations of a certain group of bands from the '70s, Dailor, on the phone from a Calgary tour stop, has no problem with that. "I think with all of our records it's kind of been threatening to go this way," he says with a chuckle. "Maybe not all the way vocally, but it definitely started showing in [the band's second album] 'Leviathan' a little bit, and then [third album] 'Blood Mountain' a whole bunch. And then this new one, the whole prog nerdiness of the group has come to light." But Dailor is quick to point out that it's "a very small window of prog, like mid-'70s: early Genesis and King Crimson and Yes and Rush."

"It's extremely self-indulgent, but it's the way we have to do it," says Dailor. "Because if you start trying to chase what you think other people want to listen to, you get lost and you're setting yourself up for disaster I think. Because what if you're wrong? Then you don't like it and they don't like it and it's over."

There was a moment that Mastodon was worried that it was over, but for different reasons. In 2007 an inebriated Hinds was seriously injured in a scuffle with another musician. He fully recovered and felt a new creative spark, which he channeled into the new album. That incident, and Mastodon's extra-curricular activities, were covered in a recent Rolling Stone feature. "That was a real bum-out, that whole thing," Dailor says of the story, which he felt put too much emphasis on the group's hard-partying ways. He says the band is not always wrecked; it couldn't play the way it does if it was. "There has to be a grounding element."

Even with its spacey theme, the new record has that musical groundedness, although some Mastodon fans have reacted to it with more head-scratching than -banging. "I can totally understand that there are fans that are not into that style of music, they're more into the super-super heavy stuff," Dailor says of message-board scorn for the new non-metal avenues. "But we have plenty of material for them to listen to if they want to go back and listen to that. But for the fans that are able to join us on the journey, then awesome."

Plenty of them have signed up for the ride: "Crack the Skye" entered the Billboard 200 last month at No. 11. "It's unique that they've gone back to an album-esque vibe but became more popular by doing it," says Gregg Steele, vice president of rock programming for Sirius/XM Radio. "Skye" is in heavy rotation on the satellite network's Liquid Metal channel, where Mastodon has always been a staple, but Steele reports that songs from the album are also making inroads on the more mainstream hard rock channel "Octane." "Ten years, 15 years ago, to even say that Genesis was an influence of yours, that would've been viewed as really uncool by metal fans," says Steele.

Dailor says the band feels a renewed vitality and hopes the riff god continues to bless them: "I think we have 50-something songs at this point, so we're always holding our breath: 'When's that well going to dry up?' Hopefully, never."

Perhaps an offering to the riff god is in order? Dailor jokes that he would be willing to sacrifice one of Kelliher's beloved "Star Wars" collectibles, agreeing that Boba Fett would probably be a good choice. There is the danger of offending the god with the wrong action figure, however. "I don't think the riff god even wants anything to do with Jar Jar Binks," he says with a laugh. "That's when you'll start hearing some really bad Mastodon songs. 'What happened to those guys? I don't know, I think they might've sacrificed Jar Jar.' "

Sarah Rodman can be reached at srodman@globe.com.