Gerrard established herself in Dead Can Dance, 1980s purveyors of melodic gloom. But on her own, she gravitates toward the stark — pairing her voice-from-beyond with portentous orchestral arrangements that move at a glacial pace. The result is something like the aural version of majesty (Gerrard’s done film scores, too, including ”Gladiator”’s). The transfixing ”Immortal,” made with classical composer Cassidy and on which she sings in Gaelic and Aramaic, won’t take her fans anywhere new. But stick with her as she builds a mystery.