Age and Geochemistry of High Arctic Large Igneous Province Tholeiitic Magmatism in NW Axel Heiberg Island, Canada

Abstract

The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada involved extrusion of continental flood basalts (CFBs) at 130–120 Ma and 100‐95 Ma and emplacement of an extensive sill and dike network that intersected the Carboniferous to Paleogene Sverdrup Basin. In this paper, we present new 40Ar/39Ar ages, major and trace elements, and Sr‐Nd‐Pb isotope ratios for HALIP lava, dikes, and sills from Bukken Fiord, NW Axel Heiberg Island, Canadian Arctic Islands. Our best constrained 40Ar/39Ar ages yield a weighted average of 124.1 ± 1 (2σ) Ma, coincident with the first pulse of tholeiitic CFB magmatism in the Arctic‐wide HALIP as exemplified by Isachsen Formation flood basalts on Axel Heiberg Island. The Bukken Fiord samples are plagioclase and clinopyroxene‐phyric tholeiitic basalts, are relatively evolved (3.2–6.5 wt% MgO), and share similar major and trace element compositions to typical HALIP tholeiites. Initial 143Nd/144Nd ranges from 0.51260 to 0.51291 and initial 87Sr/86Sr ranges from 0.70362 to 0.70776, while measured 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb range from 18.614 to 19.199, 15.534 to 15.630, and 38.404 to 39.054, respectively. The most primitive sample in this study has Sr‐Nd‐Pb isotope signatures that suggest an enriched plume‐derived mantle source for HALIP tholeiites. Most samples, however, possess relatively radiogenic isotope signatures that can be explained by moderate degrees of assimilation of Sverdrup Basin sedimentary rocks. Magma‐crust interaction in the HALIP plumbing system was likely widespread and may have increased the environmental impact of the HALIP, particularly if crustal carbon was volatilized.

Prolonged Multi‐Phase Magmatism Due To Plume‐Lithosphere Interaction as Applied to the High Arctic Large Igneous Province

“…This geochemical diversity emphasizes the unique characteristics and challenging nature of disentangling shallow‐and‐deep HALIP processes and the underlying geodynamic causes of HALIP. Do different geochemical signatures represent a different origin of melts (e.g., Tegner et al., 2011), or do they dominantly reflect shallow (crustal) processes of magma assimilation (e.g., Deegan et al., 2023)? The regional tectonic setting of HALIP, including along the Canadian margin, includes an ocean basin to rifted margin to cratonic margin setting, and has undergone several phases of tectonic events both pre‐ and post‐HALIP emplacement.…”

“…(2001), Villeneuve and Williamson (2006), and supplemented with four dates from Deegan et al. (2023). Bottom‐most bar details selected timings proposed for the opening of the Canada/Amerasia Basin including Shephard et al.…”

“…However, the significant geochemical heterogeneity makes it difficult to clearly discriminate between sources and points to one, several, or all, of the following contributions in HALIP magmas: mantle plume material of deep origin that is potentially geochemically heterogenous in nature (e.g., ocean island basalt or recycled oceanic crust signals), crustal contamination, entrainment of sub‐continental lithospheric mantle (SCLM), and/or an enriched sub‐lithospheric mantle derived from an earlier paleo‐Arctic subduction zone and slab (metasomatic signal e.g., Hadlari et al., 2018; Shephard et al., 2016). In summary, most of the analyzed volcanic rocks to‐date point to a geochemical signature that can be attributed to a mantle plume, with considerable geochemical variability potentially derived from the local interaction of the magmas with the lithosphere and crust (e.g., Deegan et al., 2023).…”