GEOCHEMICAL CONSTRAINTS ON THE ORIGIN OF CRETACEOUS BASALTS FROM THE HIGH ARCTIC LARGE IGNEOUS PROVINCE, AXEL HEIBERG ISLAND, CANADA

Mafic volcanic and intrusive rocks associated with the Cretaceous High Arctic Large Igneous Province (HALIP) are recognized across the Canadian Arctic Islands, northern Greenland, Svalbard, Franz Josef Land, and Chukchi Borderland. The origin of this Cretaceous volcanism is most likely related to the opening of the Amerasia and Eurasian Basins, however the nature of the mantle source(s) and petrogenesis of HALIP rocks remain subjects of debate. Two magmatic suites are generally proposed amongst HALIP rocks: an earlier, mantle plume-related tholeiitic suite (130 – 80 Ma) and a later, rift-related alkalic suite (85 – 60 Ma). We present new trace element and Pb-Nd-Sr isotopic compositions of 114 – 130 Ma basaltic dykes, sills, and lava flows from NW Axel Heiberg Island (AHI), Arctic Canada. All samples are tholeiitic, with high TiO₂ (2 –­ 4 wt%) and restricted variation of MgO (3.2 – 7 wt%) and SiO₂ (45 – 54 wt%) contents. They are LREE-enriched (La/Yb_(N) = 2.6 – 5) and Nb-depleted relative to Th and La. Compared with other HALIP rocks, these samples have a limited range of eNd(t) (+2.5 – 5.5), except for one lava flow with e_Nd(t) = +8.5. In contrast, Pb and Sr isotopic compositions show considerable variation (²⁰⁶Pb/²⁰⁴Pb(t) = 17.792 – 18.729; ⁸⁷Sr/⁸⁶Sr(t) = 0.70362 – 0.70778), despite acid leaching treatment prior to isotopic analyses for removal of post-magmatic alteration. Assimilation of Svedrup Basin sediments by an enriched mantle source of estimated composition similar to that of an Iceland-like mantle plume at c. 130 Ma, could account for the trace element and Nd-Sr isotopic signatures of AHI basaltic rocks. However, it cannot explain their higher ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb values at a given ²⁰⁶Pb/²⁰⁴Pb, which require an additional source component. AHI basaltic rocks are isotopically similar to metasomatized peridotite xenoliths. This suggests that variably enriched old subcontinetal lithospheric mantle was involved in the genesis of Cretaceous magmatism of AHI during the opening of the Canada Basin, and is consistent with seismic studies suggesting large amounts of exhumed subcontinental mantle in the Amerasia Basin. Further geochemical studies of HALIP related rocks are needed to constrain the composition and extent of involvement of this lithospheric source in Cretaceous Circum-Arctic volcanism.