August 2017 LIP of the Month

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The High Arctic LIP in Canada: Stratigraphic controls and geochemical monitoring on crustal influences.

Cole G. Kingsbury 1

Richard E. Ernst 1,2

Brian Cousens 1

1 Department of Earth Sciences, Carleton University, Ottawa, Canada

2 Faculty of Geology and Geography, Tomsk State University, Tomsk,

Russia

Emails: thecgkings317@gmail.com; Richard.Ernst@ErnstGeosciences.com; BrianCousens@CUNET.CARLETON.CA

This contribution reflects additional work the first author did that relates to geochemistry component of his PhD that has not been published in (Kingsbury et al., 2016). These ideas are presented in Kingsbury et al. (2017) and are being expanded into a full paper.

  1. Introduction to the High Arctic LIP

 The Cretaceous geology of Canada’s Arctic islands and formally adjacent regions of Norway and Russia are marked by widespread mafic magmatism. This magmatism manifests as a giant radiating dyke swarm, sills, and laterally extensive basalt flows including flood basalts. Together, these and the submarine equivalents of the Alpha-Mendeleev Ridge constitute the High Arctic Large Igneous Province (HALIP; Petrov et al., 2016; Saumur et al., 2016; Mukasa et al., 2015; Maher, 2001; Drachev and Saunders, 2006; Williamson, 1988; Oakey and Saltus, 2016; Buchan and Ernst, 2006; Jowitt et al., 2014; Fig. 1). HALIP in Canada is dominated in part by three pulses of tholeiitic magmas: two occurring at 120-130 Ma that fed basaltic lavas associated with the siliciclastic Isachsen Formation (Paterson and younger Walker Island Members) and a third pulse at ca. 95 – 100 Ma feeding lavas of the Strand Fiord Formation that are linked chemically to tabular intrusions in the South Fiord locality of Axel Heiberg Island (Fig. 2). Alkaline rocks, sometimes treated as part of HALIP, were emplaced beginning at 92 Ma with the Wootton Intrusive Complex (Trettin and Parrish, 1987; Estrada and Henjes-Kunst, 2013). In this contribution, we use a combination of stratigraphy and geochemistry to compare and contrast the geochemical evolution and stratigraphic characteristics of the earlier Isachsen Formation with the later Strand Fiord Formation.


Figure 1: Map of Canada’s Queen Elizabeth Islands showing the distribution and trends of mafic dykes as well as the geographic distribution of mafic lavas in the 120 – 130 Ma Isachsen Formation, c. 95 – 100 Ma Strand Fiord Formation basalts and ca. 80-85 Ma Hansen Point Volcanics. Black box indicates location of the South Fiord field area. Figure modified from Saumur et al. (2016). Key to abbreviations: A. H. = Axel Heiberg; Bjarnason Island; BM = Blue Mountain; E.R. = Ellef Ringnes; GF = Glacier Fiord ; GH = Geodetic Hills; LR = Lightfoot River; MF = Middle Fiord and SF = Surprise Fiord.


Figure 2: Geologic map of the South Fiord field area derived from SPOT-6 imagery draped on a digital elevation model (DEM). Key to abbreviation, EF = East Fiord; EFND = East Fiord North Diapir and EFSD = East Fiord South Diapir.

  1. Stratigraphy

Previous work done on the stratigraphy of the Strand Fiord Formation has shown that it represents a true continental flood basalt package (Ricketts et al., 1985; Williamson, 1988). These flows are laterally extensive, spanning 100s of km and rarely have interbeds of shales and sandstones separating individual flows. In contrast, stratigraphic work on the Isachsen Formation at Cuesta Ridge in South Fiord (this study; Fig. 3) as well as in other sections within Axel Heiberg Island, reveal that lava flows are commonly intercalated with up to 10s of m of sandstones and shales that separate individual flows (Williamson, 1988).


Figure 3: Measured stratigraphic profile of the Cuesta Ridge section of the South Fiord area showing lithology types.

  1. Geochemistry Results

Based on AFM and Nb/Y vs. Zr/Ti systematics (Fig. 4), the Isachsen Formation lavas and South Fiord intrusions, the latter which are chemically linked to the Strand Fiord Formation lavas, are subalkaline, tholeiitic basalts (Irvine and Baragar, 1971; Pearce, 2008). Mg# for Isachsen Formation lavas are 0.27 – 0.51 and 0.20 – 0.45 for the South Fiord intrusions (Fig. 5). In Ba/Nb vs. εNdt space, Isachsen Formation basalts display wide Ba/Nb ratios (~15 – 50) whereas the Ba/Nb for South Fiord intrusions tightly cluster between 15-20. South Fiord intrusions have εNdt values of+1 to +4.5, and for the Isachsen Formation flows εNdt are +2 to +6 (Figs. 5 & 6).


Figure 4: (A) AFM diagram (Irvine and Baragar, 1971) showing the compositional arrays between the Isachsen Formation lavas and South Fiord Intrusives of this study and Strand Fiord Formation lavas derived from Jowitt et al. (2014); (B) Nb/Yb vs. Th/Yb systematics (Pearce, 2008) between the Isachsen Formation lavas and South Fiord intrusives of this study.


Figure 5: Mg# vs. εNdt diagram showing the compositional arrays of the South Fiord Intrusions and the Isachsen Formation lavas. Note that the Isachsen Formation lavas have generally higher εNdt values.


Figure 6: Ba/Nb vs. εNdt diagram showing compositional arrays of the South Fiord Intrusions and the Isachsen Formation lavas. Also shown are two-component chemical models from an E-MORB starting composition towards various components of the Arctic crust: Sverdrup Basin, Franklinian Mobile Belt and the cratonic basement. From Kingsbury et al. (2016). Models are calculated using the method found in Appendix 4 of Kingsbury (2016). Sources of compositional data: For Sverdrup Basin, Patchett et al. (2004); for the Franklinian Mobile Belt and the cratonic proxy, Patchett et al. (1999); for E-MORB, Waters et al. (2011); for subducted sediments, Plank and Langmuir (1993).

  1. Discussion and conclusion

The presence of sedimentary interbeds in the Isachsen Formation but the lack thereof in the Strand Fiord Formation suggest that the recurrence interval of eruptions in the Strand Fiord Formation was much greater than that of the Isachsen Formation. Chemical modeling of Ba/Nb vs. εNdt shows evidence of contamination of the Strand Fiord basalts from underlying sedimentary rocks of the Sverdrup Basin (Fig. 6), an intracratonic basin comprised of mainly sandstones and shales that reach a depth of ~13 km (Balkwill, 1978). However, the Isachsen Formation lavas are less influenced by crustal signatures.

One possible explanation for the increased level of crustal contamination in the Strand Fiord Formation is that the higher recurrence interval of eruptions produced a larger thermal anomaly in the crust that was maintained between eruptions, that then heated the sedimentary rocks of the Sverdrup Basin. Greater heating promoted crustal contamination as hotter crust is easier to act as a contaminant than colder crust. It is possible that Isachsen Formation eruptions were infrequent enough that little to no thermal anomaly was created in the crust in the aftermath of an eruptive episode and heat was quickly dissipated between eruptions. Alternatively, lavas of the Strand Fiord Formation may have erupted at higher temperatures than lavas of the Isachsen Formation, a result to be tested in the future by geochemical modeling. Finally, further work needs to be undertaken to determine whether the contamination signature that is found in the South Fiord area can also be seen at other localities across the extent of the HALIP.

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