Timing and origin of magmatism in the Sverdrup Basin, Northern Canada—Implications for lithospheric evolution in the High Arctic Large Igneous Province (HALIP)

Abstract

Cretaceous magmatism in the Sverdrup Basin of Arctic Canada is widely considered to be part of the circum-Arctic High Arctic Large Igneous Province (HALIP). Recent studies have questioned: (i) plume involvement in the HALIP, and (ii) whether the younger magmatic events constitute the same large igneous province. We present an integrated geochemical and geochronological study to better constrain the initiation and evolution of magma genesis in the Canadian HALIP.Six new U–Pb and four 40Ar/39Ar ages of mafic lavas and intrusive sheets range from 120.9 ± 0.9 Ma to 78.4 ± 0.1 Ma, which is within the published timespan of the HALIP. The U–Pb ages are the first analyzed from the mafic intrusions of Axel Heiberg and Ellesmere Islands. The new geochronology, combined with all recently (post-2000) published ages, detail a >50 Myr duration of magmatism (128 to 77 Ma) with three main pulses. Tholeiites dominate the first 25 Myr while the latter 25 Myr consisted of coeval emplacement of alkali and tholeiitic basalts.Rare-earth-element inversion models reveal that the alkalic and tholeiitic magmas were generated beneath a bimodal lithospheric ‘lid’ thickness of 65 ± 5 and 45 ± 4 km, respectively. Whole-rock Sr–Nd isotope ratios indicate that both magma types are derived from a similar source dominated by convecting mantle. Further, these two magma types were spatially segregated by the tectonic domains of the Sverdrup Basin.We suggest that the early 128–120 Ma tholeiitic event is primarily plume-generated and correlates across the circum-Arctic with the other HALIP tholeiites. The younger magmatism, with coeval alkalic and tholeiitic magmas erupting over 25 Myr, is likely not plume-generated and may be explained by alternating modes of edge-driven mantle convection as the primary control on magma genesis. A distal plume would intensify magma production by edge-driven convection, but its influence would be secondary.