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Testing for the Sources of High 3He/4He in Failed Rift and “Plume” Related Large Igneous Provinces

J. M. D. Day
University of Durham, Department of Geological Sciences, Durham, United Kingdom

Helium, the lightest of the noble gases, can be used to trace source reservoirs with distinct isotopic characteristics. Helium has two isotopes: 4He, dominantly created by radiogenic decay of uranium and thorium, and 3He, which is primordial. A common assumption is that high 3He/4He ratios observed for many large igneous provinces (LIPs) represent a source contribution from less-degassed lower mantle. Recently this theory has come into question and shallower, upper mantle origins have been postulated.

In order to test the different hypotheses for He isotopic anomalies in mantle-derived rocks, samples from Bathurst Island (Nunavat) and the Muskox intrusion (NWT) shall be examined. This research will provide new constraints on source contribution to LIPs, analyzing 3He/4He in conjunction with Os-Sr-Nd-Hf-Pb-0 isotopes to constrain source contribution and depth of origin.

The Freeman’s Cove Eocene Igneous Province on Bathurst Island is a low-degree partial melt alkali volcanic suite related to a failed rifting event. It is an ideal area to test the source of high 3He/4He, since it forms part of the NW Atlantic incipient rift and is far enough from the Iceland “plume” to test for source derivation. The Muskox intrusion is a mafic-ultramafic body associated with the middle- Proterozoic Mackenzie LIP and is of economic interest, possessing high concentrations of precious metals. Results from the Mackenzie province will lead to clearer understanding of the role of the mantle in the evolution of the North American Craton, provide new and precise means of constraining magmatic sources, and evaluate models for precious metal mineralization.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid