Progress in Understanding the High Arctic Large Igneous Province


Marie-Claude Williamson

From Geological Survey of Canada

This presentation reviews key aspects of the tectonic and magmatic evolution of the HALIP
exposed in the Canadian Arctic Archipelago with emphasis on new data acquired by the
Geological Survey of Canada (GSC) from 2014 to present.

Located along the Canadian polar continental margin, the Sverdrup Basin is an elongated,
intracontinental sedimentary basin that originated during Carboniferous-Early Permian rifting.
During the Early Cretaceous, the Sverdrup Basin underwent tectonic rejuvenation and acquired the attributes of a volcanic basin. Over a period of ~ 45 Myr, successive magmatic episodes included the widespread intrusion of tholeiitic sills and dykes; the emplacement of continental flood basalts; the eruption of mildly alkaline, ferrobasaltic lava flows at discrete volcanic-intrusive complexes; and the emplacement of a suite of alkaline lava flows erupted from central volcanoes. The timing of igneous activity in the Sverdrup Basin Magmatic Province (SBMP) coincides with the emplacement of the High Arctic Large Igneous Province (HALIP) preserved onshore at the margins of circum-Arctic landmasses and offshore at the site of the Alpha Ridge. Remarkably, each episode is characterized by a distinctive eruptive style and coherent geochemical signature regardless of the mode of emplacement. In this context, each igneous episode of the Canadian HALIP can be viewed as a time-marker in the evolution of the Sverdrup Basin and Canadian Arctic rifted margin. However, a recent GSC mapping initiative under the Geo-mapping for Energy & Minerals Program (GEM2-HALIP, 2014-2017) reveals a more complex igneous history.

Just as the last GEM2-HALIP field season concluded, a collaborative Canada-Sweden Polar
Expedition under Canada’s ECS-UNCLOS Program dredged approximately 100 kg of volcanic rocks from the Alpha Ridge. The size and pristine state of the samples enabled the first comprehensive study of a single eruptive event in the volcanic record of the Alpha Ridge. The sample is a lapilli tuff containing vitric and basaltic clasts that record a phreatomagmatic eruption in a subaerial or shallow marine setting (depth < 80 m). A multi-fragment step heat analysis of the plagioclase-bearing basaltic glass yielded a 40 Ar/ 39 Ar plateau age of 90.40 ± 0.26 Ma (2σ error). The new age for the lapilli tuff suggests that magmatism at the site of the Alpha Ridge occurred near the end of the main phase of magmatism in the onshore HALIP corresponding to the interval 107-91 Ma.

A geodynamic model that describes the late-stage development of the Sverdrup Basin must
account for the following observations: (1) the transition from siliciclastic-dominated sequences to volcanism during the Early Cretaceous; (2) the results of recent mapping on Axel Heiberg Island; (3) new geochronological data on HALIP igneous rocks, onshore and offshore; and (4) the waning of magmatism in the volcanic rift basin as voluminous LIP-style magmatism was initiated at the Alpha Ridge. We present a summary of new results and knowledge gaps to inform future studies of the High Arctic Large Igneous Province in Canada’s Arctic.

Published Feb. 20, 2019 1:14 PM - Last modified Apr. 1, 2019 11:42 AM