Comparison of TIMS (U-Pb) and laser ablation microprobe ICP-MS (Pb) techniques for age determination of detrital zircons from Paleoproterozoic metasedimentary rocks from northeastern Laurentia, Canada, with tectonic implications

Abstract

Ages of detrital zircon grains from four samples of Paleoproterozoic metasedimentary rocks from northeastern Laurentia, Canada, analysed by thermal ionisation mass spectrometry (TIMS) and laser-ablation microprobe inductively-coupled plasma quadrupole mass spectrometry (LAM-ICP-MS), are presented and the methods compared. The TIMS results are more precise (±0.1% of age) and in the case of concordant analyses more accurate than the LAM-ICP-MS analyses (± l-2% precision), but both methods show a similar distribution of ages from each sample. Used as complimentary techniques, the combination of TIMS and LAM-ICP-MS analyses yield rapid, precise, and accurate information on the provenance of siliciclastic rocks, offering a powerful tool for the interpretation of the tectonic significance of sedimentary sequences in orogenic belts. The base of the Ramah Group, which sits unconformably on the Nain craton, contains exclusively Archean detritus, with detrital zircon ages corresponding closely to those of dated units in the Nain craton. The Lake Harbour Group, tectonically associated with the Rae craton, was deposited between 1934 ± 2 and 1834 ± 2 Ma and contains exclusively Paleoproterozoic detritus; 20% of the analysed grains are ∼ 2.3 Ga, consistent with an interpretation that the source of some of the detritus was the Rae craton. The Tasiuyak paragneiss, tectonically interleaved between the Rae and Nain cratons, was deposited between 1940 ± 2 and 1895 ± 2 Ma; most of the analysed grains in the two samples examined are > 2.1 Ga, suggesting that neither the adjacent Rae nor Nain cratons were important source areas for this detritus. This is consistent with an interpretation of the Tasiuyak paragneiss as an axially-fed accretionary complex rather than a marginal sequence associated with either the Rae or Nain cratons.