U-Pb dating of prograde and retrograde titanite growth during the Scandianorogeny

U/Pb ages of metamorphic titanite from high-grade gneisses of the Nasafjall et window in the north-central Scandinavian Caledonides record growth over an similar to 20 m.y. interval during the Late Silurian to Early Devonian, Biotite-amphibolite gneisses located near the basement-cover boundary conta in metamorphic titanite in two microtextural settings, one as lenticular gr ains distributed throughout a recrystallized matrix of metamorphic phases, and one as plate-like grains enclosed within biotite grains. These distinct morphological populations exhibit core-overgrowth relationships with compo sitionally similar cores and overgrowths, but the plate-like titanite grain s have a moth higher proportion of overgrowth and give slightly younger age s. Cores and overgrowths in both types are inferred to have formed along th e prograde (ca. 413 Ma) and retrograde (ca. 395 Ma) paths, respectively, of a single metamorphic cycle associated with the burial and exhumation of a slice of Baltic basement during the Caledonide orogeny (Baltica-Laurentia c ollision), The existence of polygenic U/Pb systematics in metamorphic titan ite demonstrates the potential usefulness of titanite to reveal multiple me tamorphic and deformational episodes, and to constrain the duration of meta morphic events.