Detrital zircon ages from the lower part of the Late Proterozoic(?) to Middle Cambrian Goldenville Group in the Meguma terrane of Nova Scotia suggest derivation from local sources in the Avalonian and Pan-African orogens on the margins of Early Cambrian Gondwana. Samples from near the top of the group show a broader distribution, including ages back to Archean. The εNd data show a corresponding trend, from slightly positive in the lower Goldenville Group to highly negative in the upper Goldenville Group and overlying Upper Cambrian to Lower Ordovician Halifax Group. The trends are consistent with deposition of the lower part of the Meguma succession in a rift, in which uplifted rift-flanks were the main source of the early basin fill, whereas subsequent thermal subsidence of rift margins allowed for more widespread sediment sourcing in younger units. The rift was possibly located between Gondwana and Avalonia, and may have been the locus for separation of Avalonia from Gondwana to form part of the Rheic Ocean.

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Analytical procedures and results: U-Pb detrital zircon geochronologyDetrital zircons were analysed at the University of Alberta Radiogenic Isotope facility. Samples were crushed and zircons were separated and concentrated by standard techniques using a Wilfley table, heavy liquids and magnetic separator. The grains were ablated using a New Wave Research UP213 Nd:YAG with aperture imaging system. The wavelength was 213 nm, with a fluence of 3 Jcm -2 , a 4 Hz pulse rate and a spot size of 40 µm. Ablated ions were analysed with a Nuplasma multicollector ICP-MS with plasma power, gas flows, detector configuration and isotope measurements as described by Simonetti et al. (2005). Results from each sample site were recorded in 30 one-second integrations after a settling time of 3 s. Blanks and standards were recorded for the same duration as unknowns.For the Southern Uplands samples, analysed first, separated zircons were picked, avoiding cracked or altered grains, and ~200 grains were mounted in an epoxy mount and polished to a depth required to approximately expose grain centres. Ablation points were selected using a combination of electron backscatter images, reflected, and transmitted light, so as to avoid obvious inclusions, discontinuities and cracks. Grains were analysed in sequences of 10 or 12, preceded and followed by at least two analyses of standards. Results were normalized using the in-house standard LH94-15 with isotopic ratios determined by thermal ionization mass-spectrometry (TIMS) as quoted by Simonetti et al. (2005), yielding a concordant age of 1830 Ma.