U–Pb zircon ages and Hf isotopic data from sedimentary and volcanic rocks in the Cobequid Highlands, Nova Scotia, Canada: implications for early history of Avalonia

New U–Pb zircon geochronology by both laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and chemical abrasion–isotope dilution–thermal ionization mass spectrometry shows that a tuff in the Folly River Formation in the Bass River block in the Avalonian Cobequid Highlands of Nova Scotia contains two large populations of Tonian zircon at c. 780 and 890 Ma. New and previously published LA-ICP-MS detrital U–Pb zircon dates from sedimentary rocks in the Folly River and Gamble Brook formations in the Bass River block and the Mount Thom Formation in the Mount Ephraim block are mainly Mesoproterozoic and early Paleoproterozoic. The similarity in spectra, with major peaks at 1000, 1200, 1500–1600, 1800 and 2000 Ma, suggests that they were derived from similar sources in Baltica. They may have been deposited in a back-arc basin associated with the first Avalonian arc represented by the 760–730 Ma volcanic rocks of the Dalhousie Mountain Formation and Mount Ephraim Plutonic Suite. Lutetium–Hf isotopic data from tuff and arkosic wacke in the Folly River Formation combined with previously published data show both positive and negative ε Hf ( t ) values and confirm previous Sm–Nd isotopic data which demonstrated that both juvenile and evolved Archean, Paleoproterozoic and Mesoproterozoic crust occurs in Avalonia.