GEOCHEMICAL INSIGHTS ON THE EARLY CRETACEOUS HIGH ARCTIC LIP

Mafic dykes, sills and lava flows, emplaced in short pulses within the interval c. 90 – 130 Ma, are exposed in Canada’s High Arctic, Svalbard Norway and Franz Josef Land (FJL) Russia. Now fragmented due to subsequent rifting about the ultra-slow Nansen-Gakkel Ridge, they represent the tectonically dismembered and eroded remnants of the once contiguous High Arctic large igneous province (HALIP).

Mapping and sampling of tabular mafic intrusions (July, 2013) on west-central Axel Heiberg Island, Arctic Canada, was done in order to characterize this set of HALIP intrusions for geochemistry, U-Pb geochronology, and assess these mafic rocks as vectors to potential Ni-Cu-PGE targets. 17 new whole-rock geochemical analyses on samples from a c. 100 – 130 Ma magmatic pulse reveal that these are sub-alkaline tholeiitic basalts with moderate TiO₂ (1.7 – 3.0), variable K₂O (0.1 – 2) and are chemically similar to E-MORB. These rocks have Tb/Yb_n < 1.8 indicating that the depth of melting was in the spinel lherzolite stability field. There is a weak anti-correlation between Ce/Yb (10 – 16) and Mg# (0.3 – 0.5) coupled with a slight negative Nb-Ta anomaly signifying that assimilation of upper lithospheric mantle and/or lowermost continental crust played a role in the geochemical evolution of these rocks.

Previous studies show that the Canadian Arctic feature two geochemical suites consisting of c. 100 – 130 Ma tholeiites (as elucidated above) and younger (c. 95 Ma) mildly alkaline rocks (ferrobasalts). From other previous studies, the Eurasian side includes two geochemically distinct suites of c. 125 Ma tholeiites on both Svalbard and FJL, and together with the Canadian occurrences reflect the interplay between depth of melting and subsequent assimilation processes. The Canadian, FJL and Svalbard tholeiitic magmas all originated in the spinel lherzolite stability field. Ce/Yb ratios of the tholeiitic basalts from Svalbard (10-12) and FJL (5 - 8) exhibit a narrow range over a large range in Mg# within each suite, whereas Ce/Yb in FJL tholeiitic basaltic andesites varies considerably from 7-21 over a modest range in Mg# (0.32 – 0.41). Thus, assimilation of crustal basement rocks is an important process in the evolution of the Canadian tholeiites and FJL tholeiitic basaltic andesites but not in the Svalbard and FJL tholeiitic basaltic rocks.