New Constraints on the Age, Geochemistry, and Environmental Impact of High Arctic Large Igneous Province Magmatism: Tracing the Extension of the Alpha Ridge Onto Ellesmere Island, Canada

Abstract

The High Arctic Large Igneous Province (HALIP) represents extensive Cretaceous magmatism throughout the circum-Arctic borderlands and within the Arctic Ocean (e.g., the Alpha-Mendeleev Ridge). Recent aeromagnetic data shows anomalies that extend from the Alpha Ridge onto the northern coast of Ellesmere Island, Nunavut, Canada. To test this linkage we present new bulk rock major and trace element geochemistry, and mineral compositions for clinopyroxene, plagioclase, and olivine of basaltic dykes and sheets and rhyolitic lavas for the stratotype section at Hansen Point, which coincides geographically with the magnetic anomaly at northern Ellesmere Island. New U-Pb chronology is also presented. The basaltic and basaltic-andesite dykes and sheets at Hansen Point are all evolved with 5.5-2.5 wt% MgO, 48.3-57.0 wt% SiO 2 , and have light rare-earth element enriched patterns. They classify as tholeiites and in Th/Yb vs. Nb/Yb space they define a trend extending from the mantle array toward upper continental crust. This trend, also including a rhyolite lava, can be modeled successfully by assimilation and fractional crystallization. The U-Pb data for a dacite sample, that is cut by basaltic dykes at Hansen Point, yields a crystallization age of 95.5 ± 1.0 Ma, and also shows crustal inheritance. The chronology and the geochemistry of the Hansen Point samples are correlative with the basaltic lavas, sills, and dykes of the Strand Fiord Formation on Axel Heiberg Island, Nunavut, Canada. In contrast, a new U-Pb age for an alkaline syenite at Audhild Bay is significantly younger at 79.5 ± 0.5 Ma, and correlative to alkaline basalts and rhyolites from other locations of northern Ellesmere Island (Audhild Bay, Philips Inlet, and Yelverton Bay West; 83-73 Ma). We propose these volcanic occurrences be referred to collectively as the Audhild Bay alkaline suite (ABAS). In this revised nomenclature, the rocks of Hansen Point stratotype and other tholeiitic rocks are ascribed to the Hansen Point tholeiitic suite (HPTS) that was emplaced at 97-93 Ma. We suggest this subdivision into suites replace the collective term Hansen Point volcanic complex.The few dredge samples of alkali basalt available from the top of the Alpha Ridge are akin to ABAS in terms of geochemistry. Our revised dates also suggest that the HPTS and Strand Fiord Formation volcanic rocks may be the hypothesized subaerial large igneous province eruption that drove the Cretaceous Ocean Anoxic Event 2.

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

“…Since LOI is low for all of the Bukken Fiord samples (<0.2 wt.%) and since they plot consistently on an immobile element classification plot (Figure 4b), we argue that the whole‐rock data overall reflect primary igneous compositions. The Bukken Fiord samples moreover show coherent trends for major element oxides (e.g., Al 2 O 3 , FeO*, CaO) and compatible elements (e.g., Ni, Sc) (Figure 5) all of which are similar to those exhibited by the bulk of HALIP basalts in the literature (e.g., Bédard et al., 2021a; Naber et al., 2021). In addition, trace and rare element patterns and trace element ratios exhibited by the Bukken Fiord samples are comparable to those previously reported for Isachsen Fm.…”

“…(2021b), Dewing & Embry (2007), Naber et al. (2021), and Pointon et al. (2019) with depositional phases after Embry and Beauchamp (2019).…”

“…To underscore this point, note that sedimentary rocks from the Sverdrup Basin (Patchett et al., 2004) plot in the upper right quadrant of Figure 8a (brown circles) with high Th/Yb for a given Nb/Yb. Previous work showed that back‐modeling the trace element compositions of HALIP tholeiites to remove the effects of fractionation and assimilation produces parental compositions within the mantle array while forward assimilation and fractional crystallization modeling was shown to reproduce the observed HALIP data (see Bédard et al., 2021a; Naber et al., 2021). Given that the Bukken Fiord data overlap exactly with Isachsen Fm.…”

“…85 Ma in Greenland (e.g., Estrada & Henjes‐Kunst, 2004; Estrada et al., 2016; Evenchick et al., 2015; Naber et al., 2021; Tegner et al., 2011). Tholeiites are the most voluminous magma type in the HALIP and their origins are widely attributed to the activity of a mantle plume impinging beneath the Alpha Ridge (e.g., Bédard, et al., 2021a, 2021b; Buchan & Ernst, 2018; Drachev et al., 2018; Embry & Osadetz, 1988; Estrada, 2015; Naber et al., 2021; Tegner et al., 2011). Among the tholeiites, two distinct pulses of magmatism have been identified—an earlier pulse represented by Isachsen Formation flood basalts at ca.…”

Volcanism‐Triggered Climatic Control on Late Cretaceous Oceans

“…OM burial exhausted the dissolved O 2 in deep seawater, causing anoxic/dysoxic conditions to develop (Jenkyns, 2010), as supported by the low Fe 3+ /Fe 2+ ratios in the black/gray shales at both sites (Figures 2 and 3). Enhanced volcanic activity during this time is consistent with a documented period of subaerial eruptions of the High Arctic Large Igneous Province (Naber et al, 2021), along with Boreal marine deposits with abundant ash beds (Grasby et al, 2021), as well as the timing of maximum extent of continental arcs (Lee et al, 2018).…”