Abstract
Ion microprobe UPb 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.
Highlights
The early stages of Iapetus Ocean closure involved formation of intraoceanic island arcs subsequently followed by subduction of continental crustal lithologies of the adjacent continents
Broadly coeval high pressure (HP) units from Svalbard may have formed by initial intra-Iapetus oceanic subduction and subsequent arc collision with a continental fragment of probable Laurentian affinity, providing a possible link between HP metamorphism in Svalbard and island arc magmatism preserved in the Pearya Terrane (e.g. Gee and Teben’kov, 2005; Labrousse et al, 2008; Majka et al, 2015)
Some of the dated samples revealed the common occurrence of inherited cores within zircon that yielded older ages ranging from Neoarchean to Cambrian. Based on this discovery we suggest that the Thores Suite records arc-related magmatism located either at the northern Laurentia margin or on a sliver of Precambrian continental crust within the Iapetus Ocean
Summary
The early stages of Iapetus Ocean closure involved formation of intraoceanic island arcs subsequently followed by subduction of continental crustal lithologies of the adjacent continents. In the North Atlantic region, evidence for this process is especially well preserved within the Middle and Upper allochthons of the Scandinavian Caledonides that bear multiple occurrences of late Cambrian/early Ordovician high pressure (HP) and island arc rocks Gee et al, 2013) These HP units are the relicts of the subducted Iapetus oceanic and Baltica continental plates, whereas the island arc lithologies represent intraIapetus suprasubduction zone magmatism. Broadly coeval HP units from Svalbard may have formed by initial intra-Iapetus oceanic subduction and subsequent arc collision with a continental fragment of probable Laurentian affinity, providing a possible link between HP metamorphism in Svalbard and island arc magmatism preserved in the Pearya Terrane Broadly coeval HP units from Svalbard may have formed by initial intra-Iapetus oceanic subduction and subsequent arc collision with a continental fragment of probable Laurentian affinity, providing a possible link between HP metamorphism in Svalbard and island arc magmatism preserved in the Pearya Terrane (e.g. Gee and Teben’kov, 2005; Labrousse et al, 2008; Majka et al, 2015)
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