U-PB GEOCHRONOLOGY OF THE HIGH ARCTIC LIP FROM AXEL HEIBERG ISLAND IN NUNAVUT, CANADA: IMPLICATIONS FOR MAGMATIC EVOLUTION OF THE STRAND FIORD FORMATION

The Cretaceous High Arctic Large Igneous Province (HALIP) represents a major mafic magmatic event that greatly influenced the geologic evolution of Canada’s Arctic Islands along with formerly adjacent Svalbard (Norway), Franz Josef Land (Russia) and offshore regions such as the Alpha Ridge. Two main tholeiitic pulses constitute the HALIP: (1) an initial pulse at ca. 120–130 Ma that in Canada is temporally associated with the Isachsen Formation basalts, and a later pulse at ca. 95 – 100 Ma, which fed extensive flood basaltic lavas of the Strand Fiord Formation. Field work completed in 2013 in the vicinity of Axel Heiberg Island’s South Fiord locality, indicates a small but complex network of sills and dykes ascribed to HALIP. U-Pb ID-TIMS baddeleyite ages for a diabase from a SSE-trending dyke in South Fiord (sample 13-CK-16) is 95.18 ± 0.35 Ma (2σ) whereas a gabbro from a >50 m sill ~7 km to the dyke’s SW (sample 13-WJA-C028-A2) is 95.51± 0.24 Ma (2σ). The two ages in tandem with the similar geochemistry of the Strand Fiord Formation lavas provide the first two precise ages that date feeders of the Strand Fiord Formation. Furthermore, the two samples are distinct from each other in terms of their Sm-Nd isotopic and Th/La trace element ratios suggesting they were derived from separate batches of magma, and by extension, fed separate eruptive episodes. Sample 13-CK-16 has an elevated Th/La ratio (0.20) compared with sample 13-WJA-C28-A2 (0.16) (Kingsbury et al. 2016 – Norwegian J. Geol. v. 96). The former has similar Th/La ratios to the upper lava sequence (Artharber Creek section) whereas the latter is more similar to the lower part of the same section and to much of the Bastion Ridge section, suggesting that much of the Strand Fiord Formation lavas erupted in a very short timeframe (~<1 Ma). Finally, with the 95 Ma age from a SSE-trending dyke we speculate a potential SSE-trending feeder system for the Strand Fiord Formation lavas. If so, then there may be common plume centre position (north of Axel Heiberg island) for the c. 95 Ma pulse as well the older 120 Ma pulse, given that dykes sharing the trend of the 95 Ma pulse have also been grouped as part of the overall radiating Queen Elizabeth swarm of likely c. 120 Ma age (i.e. feeder system for the Isachen magmatism).