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In 1984, Canada and the USSR entered into an Arctic Science Exchange agreement, an important theme of which is the comparison of the geological evolution of the Arctic regions of both countries. Before 1984, progress in understanding the geology of the Arctic was hindered by political and cultural barriers. Soviet and western scientists had not enjoyed easy access to each others' field areas, and this inhibited understanding and exchange of data. The 1984 agreement between Canada and the USSR 1 for scientific and technological exchange in the Arctic represents a major step forward in the pursuit of understanding the geology of the Arctic region. This report, on the geology of a remote and important Russian island, is a direct result of this exchange, and this cooperative effort will be a landmark in providing new constraints to regional plate tectonic models and in providing basic information to aid in exploration and evaluation of the resource potential of the Canada Basin region.

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Proterozoic rocks exposed in an anticlinorium at the centre of Wrangel Island are among some of the few exposures of Precambrian strata around Canada Basin. U–Pb zircon dating of samples collected during joint Canadian–Soviet fieldwork on the island has provided crystallization ages of [Formula: see text] on a volcanic rock, 699 ± 2 Ma on a porphyritic granite sill, and a very imprecise age of ca. 0.7 Ga on a small leucogranite. Broadly similar 600–750 Ma, mostly metamorphic, ages are known from both the Arctic Alaska and northern Chukotkan parts of what is called the Arctic Alaska – Chukotka Ancestral Plate, supporting the hypothesis that they were once a single entity. By contrast, potential Late Proterozoic equivalents in the Canadian Arctic Islands include a deeply buried and relatively undeformed seismically defined succession of hypothesized Late Proterozoic age, now at greenschist-facies metamorphic grade, and the unmetamorphosed 725 Ma Franklin mafic sills, dykes, and volcanic rocks. The differences in metamorphic and igneous ages between the Arctic Alaska–Chukotka Ancestral Plate and the Canadian Arctic Islands suggest that these two areas have fundamentally different Precambrian rocks. If so, this challenges the fundamental assumption of most paleogeographic models of the pre-Canada Basin Arctic that the two areas once formed a single continuous plate. Earlier K–Ar dates together with major unconformities in Phanerozoic successions on Wrangel Island suggest early Paleozoic orogenic events.