Magnetites of anomalous composition found in association with known Holocene tephras in Banff and Jasper national parks were originally thought to represent a new tephra of unknown origin, but were later associated with Mazama tephra at two other sites in Alberta. New data from Alberta, British Columbia, and Montana confirm the compositional variability of Mazama tephra. The range of magnetite compositions presumably was produced by an inhomogeneous magma chamber, for which there is evidence in the case of the Mazama eruption.

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