It’s been four years since Blur released 13 (Virgin), a muddled batch of songs heavily inspired by American indie rock; the once cocksure Britpoppers–who for many years battled Oasis for UK pop supremacy–seemed to be searching for a new sound. In the interim front man Damon Albarn visited Mali, where he recorded the surprisingly strong Mali Music (Honest Jon’s/Astralwerks) with a stellar cast of traditional players like Afel Bocoum, Toumani Diabate, and Lobi Traore, and struck gold with the cartoon side project Gorillaz. But when Blur finally reconvened to start recording the new Think Tank, longtime guitarist Graham Coxon didn’t show up right away, and when he straggled in several weeks later he had trouble fitting his rock licks into the looser, more groove-driven material. Frustrated, he left the sessions and the band, and he’s heard on only one of the tracks. Think Tank, marked plainly by Albarn’s recent musical excursions, is another step in the group’s transformation from cheeky pop masters to earnest musical explorers. The album effectively blends Gorillaz-style looped rhythms (two of the more extroverted tracks here were produced with Norman Cook, aka Fatboy Slim) and well-deployed African instrumentation (much of the material was recorded in Marrakech). The piercing cry of a raita wafts through a brief opening in the punkish, paranoid “We’ve Got a File on You,” and elsewhere riffs and arpeggios played on the north African oud and n’goni fill the spaces Coxon’s guitar might have occupied. Albarn’s still writing pretty melodies, but here they tend to drift through the open-ended grooves. If there’s a problem with Think Tank it’s that it’s a bit too loose–tunes like “Jets” and “Brothers and Sisters” are more vamps than actual songs. Monday, July 14, 6:30 PM, Congress Theatre, 2135 N. Milwaukee; 312-923-2000 or 312-559-1212.