PROTEROZOIC ORIGINS, PALEOZOIC TECTONICS: THE CASE 11 STORY OF THE PEARYA TERRANE AND INSIGHTS INTO ITS PLACE IN THE CANADIAN HIGH ARCTIC

Recent geochronologic and geochemical data from samples collected on northern Ellesemere Island in 2008 by CASE 11 contribute refinements to the understanding of evolution of the Pearya terrane. This work supports previous studies proposing that Pearya is a displaced fragment of the Arctic Caledonides, and reinforces correlations with other displaced fragments of Caledonide affinity across the Arctic and North American Cordillera. Proterozoic units yield data illuminating the terrane origins. Zircon U-Pb geochronology of Succession I orthogneisses reveal crystallization ages between 962 Ma-974 Ma. Trace element and Hf isotopic data from these zircon indicate an igneous arc origin for the protolith. These data suggest a connection to the Tonian subduction complex documented by other studies in the Caledonides. Detrital zircon ages from Succession II reveal three patterns: One with peaks between 1100 Ma-1800 Ma, and a young population at c. 1020 Ma; one with a c. 960 Ma age peak; and one with peaks from c. 960 Ma-1800 Ma, with young grains between 630 Ma-710 Ma. These age spectra contrast with Neoproterozoic units in the Franklinian Basin, but are characteristic of a Caledonide affinity. Data from Paleozoic units refines the tectonic chronology. A zircon U-Pb age of 539 Ma for the Ward Hunt pluton suggests links to magmatic and metamorphic activity observed in the Alexander terrane and Chukchi Borderland. A late syn-tectonic pegmatitic dike cross-cutting the fabric of Succession I in Cape Columbia crystallized at c. 453 Ma, requiring Ordovician strike-slip motion along the Pearya Shear Zone and perhaps initial terrane transport along the northern Laurentian margin. Detrital zircon age spectra from upper Ordovician to lower Silurian units reveal patterns like those observed in Succession II, and distinct from the lower Paleozoic Franklinian strata. These data provide a lower limit for the time of terrane accretion in the Silurian. Detrital zircon data from the upper Devonian Okse Bay Formation indicate a Laurentian provenance at this time, providing an upper limit for the time to terrane accretion. U-Pb ages from titanite date amphibolite facies metamorphism in Succession I at 395 to 372 Ma and support models for mid-Paleozoic accretion and sinistral translation of terranes on the northern Laurentian margin.