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 T.V. Naber1,2, S.E. Grasby1,2, J.P. Cuthbertson2, N. Rayner3, and C. Tegner4,† 1 Geological Survey of Canada–Calgary, Natural Resources Canada, Calgary, Canada 2 Department of Geoscience, University of Calgary, Calgary, Canada 3 Geological Survey of Canada–Northern, Natural Resources Canada, Ottawa, Canada 4 Centre of Earth System Petrology, Department of Geoscience, Aarhus University, Aarhus, Denmark ABSTRACT Island, Nunavut, Canada. In contrast, a new Province (HALIP), is one of the least studied U-Pb age for an alkaline syenite at Audhild of all LIPs due to its remote geographic lo- The High Arctic Large Igneous Province Bay is significantly younger at 79.5 ± 0.5 Ma, cation, and with many exposures underlying (HALIP) represents extensive Cretaceous and correlative to alkaline basalts and rhyo- perennial arctic sea ice. Nevertheless, HALIP magmatism throughout the circum-Arctic lites from other locations of northern Elles- eruptions have been commonly invoked as a borderlands and within the Arctic Ocean mere Island (Audhild Bay, Philips Inlet, and potential driver of major Cretaceous Ocean (e.g., the Alpha-Mendeleev Ridge). Recent Yelverton Bay West; 83–73 Ma). We propose anoxic events (OAEs). Refining the age, geo- aeromagnetic data shows anomalies that ex- these volcanic occurrences be referred to col- chemistry, and nature of these volcanic rocks tend from the Alpha Ridge onto the northern lectively as the Audhild Bay alkaline suite becomes critical then to elucidate how they coast of Ellesmere Island, Nunavut, Canada. (ABAS). In this revised nomenclature, the may link and influence major changes in Earth To test this linkage we present new bulk rock rocks of Hansen Point stratotype and other climate-ocean systems. major and trace element geochemistry, and tholeiitic rocks are ascribed to the Hansen The magmatism associated with HALIP con- mineral compositions for clinopyroxene, pla- Point tholeiitic suite (HPTS) that was em- sists of Cretaceous to Paleogene volcanic and in- gioclase, and olivine of basaltic dykes and placed at 97–93 Ma. We suggest this subdi- trusive units, with ages between 130 and 60 Ma sheets and rhyolitic lavas for the stratotype vision into suites replace the collective term (e.g., Corfu et al., 2013; Tegner et al., 2011; Es- section at Hansen Point, which coincides geo- Hansen Point volcanic complex. trada et al., 2016; Dockman et al., 2018; Bédard graphically with the magnetic anomaly at The few dredge samples of alkali basalt et al., 2019). Two series of HALIP magmatism northern Ellesmere Island. New U-Pb chro- available from the top of the Alpha Ridge are include: (i) a tholeiitic phase beginning at ca. nology is also presented. akin to ABAS in terms of geochemistry. Our 130 Ma and (ii) addition of an alkaline phase The basaltic and basaltic-andesite dykes revised dates also suggest that the HPTS and beginning at ca. 100 Ma and coinciding with the and sheets at Hansen Point are all evolved Strand Fiord Formation volcanic rocks may tholeiitic phase. The formation of HALIP has with 5.5–2.5 wt% MgO, 48.3–57.0 wt% be the hypothesized subaerial large igneous been suggested to be related to a mantle plume SiO2, and have light rare-earth element en- province eruption that drove the Cretaceous source but also to prolonged continental rifting riched patterns. They classify as tholeiites Ocean Anoxic Event 2. events (mainly the alkaline series) (Drachev and and in Th/Yb vs. Nb/Yb space they define a Saunders, 2006; Tegner et al., 2011; Jowitt et al., trend extending from the mantle array to- INTRODUCTION 2014; Estrada, 2015; Thórarinsson et al., 2015; ward upper continental crust. This trend, Oakey and Saltus, 2016; Estrada et al., 2016; also including a rhyolite lava, can be mod- Widespread Cretaceous magmatism report- Dockman et al., 2018). eled successfully by assimilation and frac- ed throughout the circum-Arctic borderlands The Alpha Ridge is an undersea bathymetric tional crystallization. The U-Pb data for a and within the Arctic Sea (Alpha-Mendeleev high located in the Arctic Ocean that extends dacite sample, that is cut by basaltic dykes at Ridge) is characteristic of a large igneous from northwestern Ellesmere Island, Nunavut, Hansen Point, yields a crystallization age of province (LIP) (Fig. 1) (Coffin and Eldholm, Canada across the Amerasia Basin toward Si- 95.5 ± 1.0 Ma, and also shows crustal inheri- 1994; Tarduno et al., 1998; Maher, 2001; Bry- beria, connecting with the Mendeleev Ridge tance. The chronology and the geochemistry an and Ernst, 2008; Buchan and Ernst, 2006, (Fig. 1) (Oakey and Saltus, 2016; Jackson and of the Hansen Point samples are correlative 2018; Oakey and Saltus, 2016; Jackson and Chian, 2019). The Alpha-Mendeleev Ridge is with the basaltic lavas, sills, and dykes of the Chian, 2019). A LIP is defined as a region ∼2000 km long and 400 km wide with water Strand Fiord Formation on Axel Heiberg where greater than 100,000 km3 of typically depths atop the ridge between 1000 and 2500 m basaltic magma is emplaced over a relatively and is often interpreted as a LIP, although it is Christian Tegner http://orcid.org/ 0000-0003- short duration of time (e.g., Ernst and Bleek- debated whether it is mainly an oceanic pla- 1407-7298 er, 2010). The widespread magmatism in the teau (Forsyth et al., 1986; Dove et al., 2010; †Corresponding author: [email protected]. Arctic, called the High Arctic Large Igneous Funck et al., 2011; Jokat et al., 2013) and/or GSA Bulletin; July/August 2021; v. 133; no. 7/8; p. 1695–1711; https://doi.org/10.1130/B35792.1; 14 figures; 1 table; 1 supplemental file. published online 16 December 2020 © 2020 The Authors. Gold Open Access: 1695 This paper is published under the terms of the CC-BY license. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/133/7-8/1695/5353972/b35792.1.pdf by guest on 26 September 2021 Naber et al. liamson et al., 2019a) and previously 89 ± 1 Ma (Jokat et al., 2013), (ii) ages of 127–110 Ma suggested for volcanic samples dredged at the Siberian end of the Mendeleev Ridge (Nikishin et al., 2020), and (iii) ages of ca. 118–112 Ma, ca. 105–100 Ma, and 90–70 Ma for dredge samples of the Chuckchi borderland (Mukasa et al., 2020). The compositions of the few dredged samples of the Alpha Ridge, with the exception of Van Wagoner et al. (1986), have only been reported in abstracts without access to the whole rock data. Recent interpretations of aeromagnetic and geological data (Oakey and Saltus, 2016; Estrada et al., 2016) show that magnetic anomalies of the Alpha Ridge extend onto the coastal areas of the northern Canadian Arctic Islands (Fig. 1), corroborat- ing the original ideas of Embry and Osadetz (1988) that volcanic rocks exposed there are an on-land extension of the ridge. In the Yelverton Bay area of Ellesmere Island, a magnetic anom- aly coincides with outcrops of lavas and dykes and with the Wootton intrusive complex (WIC) (Estrada et al., 2016). In addition, the ages re- ported for this magmatism (Estrada et al., 2016) partly overlap those of the Alpha Ridge. These connections still remain tenuous due to sparse chronological and geochemical studies of these different volcanic complexes. To throw new light on the petrology, chronol- ogy, and correlations of Cretaceous magmatism of northern Ellesmere Island we carried out new Figure 1. Bathymetric map of the High Arctic region showing the extend of on-land and field work and sampling in the Hansen Point area. offshore areas with magmatic rocks ascribed to the High Arctic Large Igneous Province This is the stratotype of volcanism in northern (HALIP), and the location of the study area at Hansen Point, northern coast of Ellesmere Ellesmere Island (Trettin and Parrish, 1987), but Island, Canada. The expressions of HALIP magmatism includes lavas, sills, and dykes of remains understudied due to the remote location. the Canadian Islands (Trettin and Parrish, 1987; Estrada et al., 2016; Buchan and Ernst, Here we describe the petrography, mineralogy, 2018), the De Long Islands (Nikishin et al., 2020), Franz Josef Land, Svalbard, the Barents geochemistry, and geologic history of basaltic and Sea (Polteau et al., 2016), North Greenland (Thórarinsson et al., 2015), and the High Arctic basaltic andesite dykes and sheets, and a rhyolite Magnetic High Domain interpreted as the geophysical manifestation of magmatic intrusions lava at Hansen Point. We also present new U-Pb and extrusions associated with the Alpha-Mendeleev ridge (Oakey and Saltus, 2016). Also ages for the original sample at Hansen Point dated shown are the approximate locations of offshore samples (black squares) from the Alpha by Trettin and Parrish (1987) and for a sample col- Ridge by Jokat (2003; labeled 1) and Van Wagoner et al. (1986, labeled 2). Bathymetry and lected by us at Audhild Bay, northwestern Elles- topography from Jakobsson et al. (2008). mere Island. We then classify the magma types of the mafic and felsic rocks at Hansen Point, discuss their petrogenesis and model the roles of fraction- associated with extended continental crust of the Sea (UNCLOS) studies, and have con- al crystallization and crustal assimilation. This is (Døssing et al., 2013; Oakey and Saltus, 2016; firmed the alkaline character and documented followed by a discussion of correlations and no- Petrov et al., 2016; Jackson and Chian, 2019). textures consistent with explosive basaltic vol- menclature of magma types and chronology with There are only a few dredge samples avail- canism (Massey et al., 2019; Williamson et al., previous work on (i) basalts from other occurrenc- able from the Alpha Ridge.