Volcanism in the Canadian Arctic and North Greenland related to the opening of the Arctic Ocean

Report of the project:

• CASE – Circum-Arctic Structural Events

Fig. 1: Manifestations of Cretaceous to Tertiary volcanic rocks in the Canadian Arctic and North Greenland Source: BGR

The German Federal Institute for Geosciences and Natural Resources of Germany (BGR) investigates volcanic rocks at the passive continental margins of the Arctic Ocean as part of the CASE projects (CASE = Circum-Arctic Structural Events). The examined volcanism is strongly connected with the geotectonic evolution of the northern polar region since Cretaceous times, and can give important time marks for the opening of the Arctic Ocean basins. The current works are targeted at the Canadian and Greenland margins (Fig. 1). Part of the rock samples were collected during CASE expeditions (to North Greenland in 1994, to northern Canadian Ellesmere Island in 1999, 2000, and 2001), while another part was made available by the Geological Survey of Canada, Calgary (Fig. 2). The rocks are being investigated for their petrography, geochemistry, isotope chemistry and radiometric age at BGR.

1 Volcanic rocks investigated

Along the Canadian margin, basaltic rocks were emplaced as flows, volcanic breccia, dykes, and sills during the Early Cretaceous to Cenomanian (Fig. 1). Examples given:

• Basalts of the Isachsen Formation on Axel Heiberg Island and Ellesmere Island,

  main phase during the Aptian, up to 230 m thick, with intercalated clastic fluvial sediments (Embry & Osadetz 1988)

• Basalts of the Strand Fiord Formation on Axel Heiberg Island,

  upper Albian to lower Cenomanian, up to nearly 800 m thick, mainly subaerial flows, underlain and overlain by marine shales (Ricketts et al. 1985, Embry & Osadetz 1987)

• Basalts of the Hassel Formation on northeastern Ellesmere Island,

  interbedded with non-marine sandstone and shales, up to 35 m thick, stratigraphically comparable with the Strand Fiord Formation (Osadetz & Moore 1988).

Fig. 2: Volcanic rock sample sites in the Canadian Arctic Source: BGR

Occurrences of bimodal, partly alkaline igneous rocks are known from the northernmost coast of Greenland and from the northern coast of Ellesmere Island (Fig. 1). They have been emplaced during the Late Cretaceous to early Tertiary.

• Hansen Point volcanics on northwestern Ellesmere Island,

  an about 1000 m thick sequence of flows, pyroclastic rocks, and intercalated fluvial and marine clastic sediments and coal, unconformably overlying the Permo-Carboniferous (Trettin & Parrish 1987);

• Wootton Intrusive Complex on northwestern Ellesmere Island,

  a northeast-southwest trending zone of gabbro, minor granitoids and transitional rocks, crossing the Wootton Peninsula, dated as 92 Ma (Trettin & Parrish 1987);

• Kap Washington Group volcanics in North Greenland,

  an about 5 km thick sequence of flows, pyroclastic rocks, and minor clastic sediments, concordantly overlying Lower and Upper Cretaceous and Permo-Carboniferous, overthrust by lower Paleozoic meta-sediments (Dawes & Soper 1970, Brown & Parsons 1981, Soper et al. 1982, Brown et al. 1987);

• Pebbles of volcanic rocks are present in lower Tertiary (Paleocene) sediments, which are deposited into small basins along the west coast of Nares Strait (Miall 1982).

2 First results

First results of our investigations were presented in 1998 during ICAM III held in Celle, Germany (Estrada et al. 1998, Estrada 1998), during the conferences of Deutsche Mineralogische Gesellschaft held in Vienna in 1999 (Estrada et al. 1999 a) and in Heidelberg in 2000 (Estrada et al. 2000), and during the International Polar Conferences of Deutsche Gesellschaft für Polarforschung held in Dresden in 2001 (Estrada et al. 2001) and in Jena in 2005 (Estrada et al. 2005). Currently, detailed results are published in: Estrada (1998), Estrada et al. (1999), Estrada & Henjes-Kunst (2004), and Estrada et al. (2003).

2.1 Early Cretaceous (to earliest Late Cretaceous) volcanism

Despite the difference of about 15 to 20 million years between the extrusion of the basalts of the Isachsen and Strand Fiord formations, they are very similar with respect to their petrography, chemistry, and Nd and Sr isotopic ratios. The fine-grained, intergranular to subophitic, weakly porphyritic rocks consist mainly of plagioclase and clinopyroxene. Olivine and glass appear in small amounts in the matrix. Plagioclase and rarely clinopyroxene appear as phenocrysts . The basalts are tholeiitic rocks relatively rich in TiO₂ (1.6 to 3.7 wt%), with incompatible elements such as Sr, K, Ba, Nb, P, Zr, Ti enriched relative to normal mid-ocean ridge basalts (N-MORB), and with Zr/Nb ratios between 6 und 15. Thus, their chemistry is similiar to continental flood basalts. The only remarkable difference in trace element chemistry between the the basalts of the two formations is the higher Cu content of the Isachsen Formation basalts with an average of 133 ppm (34 samples) compared to 64 ppm (26 samples) for the Strand Fiord Formation basalts. Initial positive epsilon-Nd values of 1.4 to 4.8 combined with Sr isotopic ratios of 0.7054 bis 0.7072 indicate a depleted mantle melt origin (Estrada & Henjes-Kunst 2004).

The Hassel Formation basalts are generally characterized by relatively high contents of Fe (14.0 - 16.9 wt% Fe₂O₃ total), Ti (3.0 - 3.8 wt% TiO₂), and K (0.8 - 1.5 wt% K₂O). They can be divided into two groups. A first, P rich (1.2 wt% P₂O₅) western group comprises a basalt occurrence north of Lake Hazen (between Cuesta Creek and Mesa Creek) and another one east of the Turnabout Glacier tongue, 35 km away from the former (Fig. 3). A second, eastern group is poorer in P (0.34 - 0.41 wt% P₂O₅), comprising the basalt occurrences south of Piper Pass (Fig. 4) and between Eugene and South Wood Glaciers (Fig. 5), about 25 km to the northeast of the former. The mainly fine-grained, aphyritic, intergranular to subophitic (in the western group also hypocrystalline, intersertal) rocks consist of plagioclase, clinopyroxene, olivine and glass.

Fig. 3: Basalts of Hassel Formation east of Turnabout Glacier (northern Ellesmere Island) - eroded relics of large basaltic sheets of Cretaceous age. Mountain chain in the background: Paleozoic rocks thrusted over Mesozoic rocks. Source: BGR

Fig. 4: Basalt south of Piper Pass (northern Ellesmere Island), overlying light-colored Hassel Formation sandstone Source: BGR

Fig. 5: Basalts between Eugene Glacier and South Wood Glacier (northern Ellesmere Island) (view towards the east), in the past probably linked with the basalt sheet situated farther southeast (see Fig. 4). Source: BGR

The age of the Isachsen Formation basalts, Strand Fiord Formation basalts, and Hassel Formation basalts is relatively well known due to intercalated, biostratigraphically well defined sediments. Tarduno et al. (1998) determined an Ar/Ar plateau age of 95 Ma for the Strand Fiord Formation basalts. New radiometric data are currently being determined by BGR.

2.2 Late Cretaceous to earliest Tertiary volcanism

Fig. 6: Kap Washington (north Greenland): collecting alkaline volcanic rock samples Source: BGR

The volcanism of North Greenland (Kap Washington volcanics, Fig. 6) and the Canadian Arctic (Hansen Point volcanics, Fig. 7) is bimodal and partly alkaline. Primitive compositions comprise alkali-olivine basalts, picrobasalts, basanites to trachybasalts. Chemically evolved members are represented by trachyandesites, trachytes, and rhyolites and are partly peralkaline. The basic volcanics are mostly porphyritic and amygdaloid. They have a fine- to medium-grained, intergranular matrix, consisting of plagioclase, clinopyroxene, olivine (not in the trachybasalts) and partly some glass. Phenocrysts are olivine, plagioclase, and clinopyroxene. In the porphyritic trachytes, both the fine-grained matrix and the phenocrysts consist of alkali-feldspar and plagioclase. The rhyolites have a porphyritic, felsitic, spherolithic or eutaxitic structure, are nearly completely devitrified and consist mainly of quartz and alkali-feldspar. Additionally, peralkaline rhyolites and trachytes bear alkali-amphibole and alkali-pyroxene. Geochemically, the volcanics show an intra-plate affinity.

The Kap Washington Group is intercalated with Upper Cretaceous (Campanian to Maastrichtian) shales (Batten et al. 1981). Previous studies by Larsen (1982) and new Rb/Sr whole rock dating carried out by BGR, yielded an age of 64 ± 3 Ma for the rhyolites, confirming that the volcanic activity lasted until earliest Tertiary. Ar/Ar incremental-heating experiments on an amphibole concentrate from a rhyolite yielded a minimum age of 38 Ma (Eocene), which is interpreted to date a hydrothermal overprint of the volcanic rocks during compressive tectonics (Estrada et al. 1999 b).

Fig. 7: Hansen Point (northern Ellesmere Island, Canada): blue rhyolite Source: BGR

Biostratigraphically, the age of sediments intercalated with the Hansen Point volcanics is possibly Turonian to Maastrichtian (Embry 1991). A rhyolite dated to 88 +20/-21 Ma (U/Pb zircon age), contains inherited zircon from an 1.15 Ga old source (Trettin & Parrish 1987). New Rb/Sr whole rock dating carried out by BGR on 4 trachytes and peralkaline rhyolitic ignimbrites, yield 80 ± 2 Ma (Campanian). Preliminary K/Ar whole rock dating on one sample gave an age of 64 Ma (Estrada & Henjes-Kunst 2004).

The basalts of both occurences have initial epsilon-Nd values of 1.4 to 5.9 and Sr isotopic ratios of 0.7023 to 0.7057. The Hansen Point trachytes to rhyolites have similiar values: 1.5 to 5.1 and 0.7037 to 0.7041, respectively. These values show that the rocks have been formed by melts of a common origin, a mantle reservoir slightly enriched in incompatible elements. Lower epsilon-Nd values (-4 to 0.5) and higher Sr isotopic ratios (0.7046 to 0.7066) for the Kap Washington rhyolites suggest chemical modification of the mantle derived melts by assimilation of lower crustal rocks.

2.3 Dykes and sills

Fig. 8: Sills in Triassic sediments northeast of Eureka station (Ellesmere Island) Source: BGR

Basaltic dykes and sills are widespread in the surroundings of all volcanic suites. Because of their petrographical and geochemical similarity, the sills and dykes within Mesozoic sediments near the Eureka station on Ellesmere Island could be intrusive equivalents of the Isachsen Formation basalts (Fig. 8). Age determinations are not available yet.

3 Plate tectonic interpretation

Fig. 9: Paleogeographic reconstruction for the Late Cretaceous: volcanism before the opening of the Eurasian Basin Source: BGR

During Cretaceous times, North America, Greenland, and Eurasia were part of a common land mass. While the Canada Basin was already opening, the Eurasian Basin of the Arctic Ocean and the North Atlantic were still closed. Episodic volcanic activities announced the break-up of this super-continent and the opening of the new ocean basins at the beginning of the Tertiary (Fig. 9).

The Early Cretaceous (to earliest Late Cretaceous) basalts in northern Canada probably erupted together with chronologically and chemically similiar volcanics of Franz Josef Land (e.g. Campsie et al.1988, Bailey & Brooks 1988, Dibner 1998, Ntaflos & Richter 1998) and Svalbard (e.g. Burov et al. 1977, Maher 1999) forming a large continental flood basalt province. Tarduno (1998) has labelled this province "High Arctic Large Igneous Province".

The bimodal, partly alkaline volcanic suites of northern Canada (Hansen Point volcanics) and North Greenland (Kap Washington Group) have possibly been formed in a failed rift branch of a large continental rift zone, preceding sea floor spreading in the Eurasian basin of the Arctic Ocean that started about 56 Ma ago (Srivastava & Tapscott 1986).

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