Ten luxuriant, often dark songs ranging from Martian electronica to inimitable balladry to id-channeling reveries, with African percussion, thick brass and deeply emotional singing: That’s Bjork’s new album in a nutshell, and, as usual, she sounds like no one but herself. Volta is arguably Bjork’s loosest and most ruminative record, and though it touches on everything she’s ever done, it’s not as gripping or coherent as her best stuff, notably 2001’s Vespertine. But with help from well-picked collaborators, including Timbaland and Malian kora player Toumani Diabate, the gratuitously detailed new disc packs some great moments. Two Timbaland-produced cuts — “Innocence” and the rumbling, percussion-laden opener, “Earth Intruders” — are the closest thing to instant pleasures. But Bjork is at her best on two flights of fancy: “Hope,” a gorgeous thing that ponders suicide bombers and features some of her tenderest, most agile singing ever, and the terrific “I See Who You Are,” a swirl of Asian strings and swooning melodies that seems to be about sex. Overall, a pretty good argument for Bjork to keep doing whatever she pleases — not that she ever wouldn’t.