No abstract

No abstract

The Cretaceous geological evolution of the Canadian Arctic was marked by voluminous magmatism comprising Canada's portion of the High Arctic large igneous province (HALIP) that is thought to have resulted from a mantle plume head. This magmatism is largely recorded as extensive Early Cretaceous lavas of the Isachsen Formation, Late Cretaceous continental flood basalts of the Strand Fiord Formation, and an extensive network of dykes and sills forming their plumbing systems. Axel Heiberg Island near South Fiord contains a small, structurally complex portion of the overall network of HALIP tabular intrusions, from which samples from the South Fiord intrusions and Isachsen Formation basaltic lavas were analysed to better understand their petrogenesis. Specifically, we apply trace-element ratios together with Sm-Nd isotope systematics in order to identify processes that shaped the chemical evolution of the South Fiord intrusions and Isachsen Formation lavas, to identify (1) mantle source chemistries and (2) the role of crustal assimilation. On the basis of Sm-Nd isotopic results, South Fiord intrusion magmas were derived from a homogeneous mantle source whereas a more heterogeneous source is invoked for the Isachsen Formation lavas. Furthermore, modelling with Th/ La, Nb/U, Ba/Th and Ba/Nb suggests that South Fiord intrusive magmatism was contaminated by sedimentary rocks from the Sverdrup Basin. Conversely, a trend towards high Ba/Th in Isachsen Formation lavas suggests a subducted sediment component derived from extinct subduction zones. We surmise that (1) South Fiord intrusive rocks are geochemically distinct from the Isachsen Formation lavas and (2) the HALIP mantle plume head intersected and incorporated sediments from ancestral subduction zones to the present-day Aleutian and Alaska subduction zones to produce the Isachsen Formation flows, whereas the South Fiord intrusions (and correlated Strand Fiord magmatism) were generated from plume material that interacted with upper crustal sedimentary rocks.

No abstract

The Cretaceous to Paleogene High Arctic Large Igneous Province (HALIP) occurs in circum-Arctic regions, and the largest portion of the province occurs in Canada’s Arctic Archipelago. This paper reviews and documents the geometry and distribution of the Canadian portion of the HALIP, focussing most notably on the architecture of its intrusive component. The extent of dyke swarms and sills of the Canadian HALIP is updated and is shown to be greater than previously acknowledged. Sills, in particular, occur throughout the Sverdrup Basin and crop out extensively on Axel Heiberg Island within Triassic to Cretaceous strata. The HALIP event is dominantly intrusive, with 3–5 times more intrusive rocks than extrusive rocks, by volume. There is local evidence of syn-emplacement fault activity, possibly involving the reactivation of older faults, controlling the emplacement of dykes. In the eastern Sverdrup Basin, exposures of components of the HALIP are controlled by tectonic elements of the Eocene Eurekan Orogeny, with plumbing systems (dykes, sills) exposed along regional-scale anticlines or the hanging walls of thrusts. Portions of the HALIP have been shown to be prospective for magmatic Ni – Cu – platinum group elements (PGEs) based on geochemistry, and although geochemical controls play a critical role in the genesis of such deposits, structural and magma dynamic controls are also important to consider at the scale of 1–10 km magmatic complexes. Underpinned by the architecture of the Canadian HALIP, we document the structural characteristics of three 1–10 km-scale volcanic–intrusive complexes of the province that show Ni–Cu–PGE prospectivity: the volcanic–intrusive complex of the Strand Fiord – Expedition Fiord area, the Surprise Fiord dykes, and the Wootton Intrusive Complex. All three represent physico-structural environments that would likely promote high magma flowthrough and sulphide transport, and could be targeted for Ni–Cu–PGE magmatic sulphide mineralization.