Geochemical and Sr–Nd isotope variations within Cretaceous continental flood-basalt suites of the Canadian High Arctic, with a focus on the Hassel Formation basalts of northeast Ellesmere Island

Abstract

Early- to mid-Cretaceous flood-basalt suites of the northeast Canadian High Arctic assigned to a High Arctic Large Igneous Province (HALIP) were studied for their whole-rock geochemistry and Sr–Nd isotopes. Data from basalt flows within the upper Albian to lower Cenomanian Hassel Formation of northeast Ellesmere Island are compared with former published data and new inductively coupled plasma mass spectrometry data of the stratigraphic equivalent Strand Fiord basalts and the older, late Hauterivian to Aptian Isachsen basalts from Axel Heiberg Island. The transitional to mildly alkaline aphyric Hassel basalts, with ocean island basalt (OIB)-like geochemical signatures in parts, have an Ar–Ar whole-rock age of on average 96.4 ± 1.6 Ma. They represent two geochemically different flow units without a fractional crystallization relationship: the high-phosphorous (HP) and low-phosphorous (LP) basalts. The Hassel HP basalts differ from the LP basalts by additionally higher Ba, K, Rb, Th and LREE contents, a pronounced positive Eu anomaly (Eu/Eu* = 1.74–1.76), as well as lower Ta, Nb, Zr and Hf concentrations. The Nd and Sr isotope ratios of the Hassel HP basalts [e Nd(t) of −1.3 to −1.4, 87Sr/86Sr(t) of 0.70706–0.70707] and the LP basalts [e Nd(t) of 4.5–4.9, 87Sr/86Sr(t) of 0.7038–0.7040] indicate an origin from different mantle sources. The geochemically similar tholeiitic Isachsen (ca. 130–113 Ma) and Strand Fiord basalts (ca. 105–95 Ma) are also incompatible element enriched relative to the primitive mantle, however, with negative Sr–P anomalies as well as partially negative K, Ta and Nb anomalies. In terms of incompatible element ratios (Zr/Nb, Nb/Th), several mantle components are involved in the formation of the flood-basalt suites: a component with primitive mantle composition, an OIB-like component (probably subducted and recycled oceanic crust) and an enriched lithospheric component. The latter component, probably metasomatized subcontinental lithospheric mantle, has contributed mainly to the Isachsen, Strand Fiord and Hassel HP basalts. In the Sr–Nd isotope system, the enriched lithospheric component is characterized by hypothetical values of e Nd(t) of approximately −4, and 87Sr/86Sr(t) of approximately 0.7083. The HALIP-related flood-basalt suites of the Canadian High Arctic are interpreted to be part of a continental rift zone that was active during the opening of the Amerasia Basin of the Arctic Ocean and the development of the oceanic Alpha-Mendeleev Ridge into a Large Igneous Province.