New constraints on the timing of deposition and metamorphism in the Bamble sector, south Norway: Zircon and titanite U-Pb data from the Nelaug area

In order to further constrain the deposition of supracrustal suites and metamorphism in the Bamble sector, south Norway, zircon and two generations of titanite from the granitic to granodioritic Nelaug Gneiss have been dated. The Nelaug Gneiss, situated along the Porsgrunn-Kristiansand Fault separating the Bamble from the Telemark sector, cuts the supracrustal Selås Banded Gneisses. Four discordant zircon fractions from the Nelaug Gneiss yield an upper intercept age of 1460±21 Ma, interpreted as the age of magmatic emplacement of the protolith of the Nelaug Gneiss, underlining the importance of the 1.5-1.4 Ga interval in the formation of the crust of the western part of the Southwest Scandinavian Domain. The presently available data show that there were two periods of sedimentation in the Bamble sector, an older around 1.45 Ga related to sedimentation in two distinct settings, and a younger period postdating 1.37 Ga. The 1091±2 Ma age of subhedral orange-red titanite is in agreement with previously obtained ages for peak Sveconorwegian metamorphism in the coastal part of the Bamble sector. The 994±30 Ma age of anhedral beige titanite correlates with the p-T path of the Nelaug area which, in contrast to the p-T path of the coastal area, reveals a late increase in metamorphic conditions in the latter area.