CHEMICAL FINGERPRINTING OF CRETACEOUS BENTONITES IN CANADIAN ARCTIC BASINS: INVESTIGATION INTO THEIR POTENTIAL MAGMA SOURCES

Bentonites are abundant throughout the Cretaceous stratigraphic sections of western and northern North America with bentonite swarms characterizing the Upper Cretaceous. Thirty bentonites collected from Cretaceous sections across the eastern (Ellef Ringnes and Axel Heiberg islands, Sverdrup Basin) and western (Anderson Plain, Yukon Coastal Plain, Eagle Plain) Canadian Arctic, as well as the Western Interior Basin are used to evaluate the geochemical signatures of volcanism over space and time. U-Pb zircon geochronological studies on select bentonites yield ages between 83 Ma to 111 Ma, with most in a more restricted interval between 88 and 93 Ma. Geochemical analysis of bentonites, as well as melt inclusions within zircon phenocrysts is used to characterize the magma source and infer tectonic origin of the volcanic ash. Tectonic discriminant analysis based on trace elements show that Eastern Arctic bentonites have intra-plate volcanic signatures, whereas Western Arctic and Western Interior bentonites have a more complex subduction-related signature. Eastern Arctic bentonites of the Aptian to Albian Christopher Formation and latest Cenomanian to Campanian Kanguk Formation on Axel Heiberg Island show no significant geochemical variation despite spanning 28 Ma. The compositions of Eastern Arctic bentonites show affinity to geochemical signatures found in extrusive volcanic samples of the Cretaceous High Arctic Large Igneous Province (HALIP), and the bentonites are interpreted to be derived from HALIP volcanism. In contrast, Western Arctic bentonites likely relate to continental arc volcanism occurring at the Pacific margin of North America. Microprobe analysis of glass inclusions within zircon phenocrysts confirmed a rhyolitic melt for the Eastern Arctic bentonites whereas evidence for a basaltic melt was detected for a Western Arctic bentonite sampled on Eagle Plain. Comparison between bentonites of nearly comparable age sampled on Ellef Ringnes and Axel Heiberg islands shows differences in their elemental composition suggesting bentonites as a correlation tool in this area may be possible.