MAGMATISM AT THE NEOPROTEROZOIC-CAMBRIAN BOUNDARY IN THE PEARYA TERRANE (NORTHERN ELLESMERE ISLAND) REVEALED BY ZIRCON U-PB, LU-HF, AND TRACE ELEMENT ANALYSES OF THE WARD HUNT PLUTON: A POSSIBLE MAGMATIC LINK BETWEEN THE CALEDONIDES AND THE TIMANIDES?

The Pearya terrane (northern Ellesmere Island) is a displaced crustal fragment with strong lithologic and geochronologic similarities to Svalbard and the East Greenland Caledonides, that was emplaced along the Franklinian margin of Laurentia during the Paleozoic. The composite Pearya terrane contains a documented record of earliest Neoproterozoic and middle-late Ordovician arc magmatism. The Ward Hunt pluton, a syenite-monzodiorite intrusive complex on Ward Hunt Island, records an additional magmatic phase within the Pearya terrane. The plutonic complex intrudes metasedimentary units included in the Pearya terrane; both of these units are in fault contact with Carboniferous-Permian Pearya strata. Zircons separated from the syenite phase of the pluton display simple igneous zoning with extensive mottled domains suggestive of metamictization. U-Pb SIMS (USGS-Stanford SHRIMP-RG) data from zircon with preserved zoning defines a concordia age of ca 539 Ma. No inherited zircon grains or cores are observed. LA-ICPMS (Arizona LaserChron Center) Hf isotopic data from zircon yielding U-Pb ages in this range yield dominantly positive εHf_{(539 Ma)} values, ranging from -1.4 to +10.2 and suggestive of a relatively primitive source. SIMS trace element geochemistry of unaltered zircon domains is consistent with normal magmatic growth with little input from metamorphic or anatectic fluids, or by extensive fractionation processes. Latest Neoproterozoic-earliest Cambrian magmatism is not common in Caledonian terranes thought to be correlative with the Pearya terrane, but is recorded by igneous and detrital zircon ages observed in other terranes in the Circum-Arctic region (e.g., Alexander terrane, Arctic Alaska-Chukotka terrane, and the Timanides). The presence of the Ward Hunt pluton extends ties of the Pearya composite terrane beyond Svalbard and East Greenland, and in conjunction with late Neoproterozoic-early Cambrian detrital zircons present in the sedimentary successions of the terrane, suggests additional ties to Timanide terranes.