Diffusive Isotopic Contamination of Mafic Magma by Coexisting Silicic Liquid in the Muskox Intrusion

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Abstract
Shifts in 87Sr/86Sr and 143Nd/144Nd ratios measured in cumulates from the upper levels of the Muskox mafic intrusion indicate that isotopic and bulk chemical exchange were decoupled across a mafic-silicic liquid interface during crystallization of the intrusion. Modeling of diffusive exchange between liquid layers demonstrates that isotopic compositions of silicate liquids in layered magma chambers may be strongly affected by this process on time scales of 103 to 104 years. Diffusive contamination can be used to place constraints on the physical processes and time scales of magmatic systems.