Abstract

This paper presents age determinations on six units of the Franklinian deep-water basin and the Pearya Terrane of northern Ellmere Island and discusses their tectonic implications.Four different fractions of detrital zircon from the Lower Cambrian Grant Land Formation of the deep-water basin all have average 207Pb/206Pb ages of 2.2–2.4 Ga, suggesting that the sediments were derived mainly from Aphebian–Archean parts of the Canadian Shield rather than from the Neohelikian crystalline basement of Pearya, as assumed earlier. The first evidence for Ordovician arc-type volcanism in the northern part of the deep-water basin is provided by a Llandeilo(?) zircon age of graphic but the fault-bounded volcanic unit could be exotic.Four major stratigraphic successions are recognized in Pearya. Present zircon studies confirm that succession I has been affected by a 1.0–1.1 Ga orogeny, as inferred earlier by Sinha and Frisch from a Rb–Sr isochron. A zircon age of graphic on a rhyolite demonstrates that succession II extended into the Late Cambrian or Early Ordovician.Granitic intrusions in the Pearya Terrane, at Cape Richards and Cape Woods, are, respectively, Middle Ordovician (463 ± 5 Ma) and Devonian (382 ± 18 Ma or, more likely, 390 ± 10 Ma) in age on the basis of combined zircon and sphene determinations. They are post-tectonic with regard to major deformations in the Middle Ordovician and Late Silurian. Both have a significant component of xenocrystic zircon, which appears to have been derived from succession I of Pearya on the basis of upper intercept ages.

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