The Ordovician Thores volcanic island arc of the Pearya Terrane from northern Ellesmere Island formed on Precambrian continental crust

Ion microprobe U-Pb zircon dating of intermediate to felsic rocks coupled with bulk-rock geochemistry analyses and compared to previously published data shows that the Thores Suite of the Pearya Terrane of northern Ellesmere Island (Arctic Canada) represents an Early Ordovician (c. 490-470 Ma) suite formed in an island arc setting. Interestingly, three out of five dated samples contain abundant xenocrystic zircon that have ages spanning from c. 2690 Ma to c. 520 Ma. The vast majority of xenocrystic zircon are Precambrian in age and typical of Laurentia. The youngest well-pronounced age cluster around 580-570 Ma is inferred to be an expression of the Timanide Orogen, traditionally ascribed to Baltica. This geochronological dataset provides new insight on the origin of the Thores Suite of the Pearya Terrane, which was traditionally thought to be formed due to the M'Clintock orogenic event and commonly treated as independent from Caledonian tectonism. We suggest that the Thores island arc formed on a sliver of continental crust within the Iapetus Ocean. The timing of igneous activity recorded by the Thores Suite is consistent with other island arcs and subduction-related metamorphic units that occur within the Caledonides of northern Scandinavia and Svalbard. Hence, we suggest that the Thores volcanic island arc was closely associated with age equivalent arcs developed within the northern Iapetus Ocean. Its juxtaposition with the other successions of the Pearya Terrane is explained by a large-scale, left lateral, strike-slip system operating along the northeastern margins of Baltica and Laurentia, coeval with the main collision between the two continents. This strike-slip system was responsible for the juxtaposition of multiple terranes with contrasting Precambrian histories that can be traced in the present day High Arctic, e.g. in southwest Svalbard and the Pearya Terrane.

Automated summary

The Thores Suite in the Pearya Terrane of Arctic Canada was formed in an island arc setting during the Early Ordovician period. The presence of xenocrystic zircon with Precambrian ages, typical of Laurentia, suggests a complex geological history for this region. The geochronological dataset reveals insights into the formation of the Thores Suite and its connection to other tectonic events in the Caledonides of northern Scandinavia and Svalbard.