Abstract

A 525-m-long drill core (DDH-221) through the Partridge River intrusion in northeastern Minnesota consists of mesocumulates and/or orthocumulates of troctolite, olivine gabbro, and olivine gabbronorite. The cumulus olivine, whose composition (Fo31 to Fo71) is a function of the amount of intercumulus liquid, followed an equilibrium crystallization path with this liquid. Estimates of the primary magmatic compositions of the olivine are Fo57 to Fo79. None of the olivine in the drill core samples has retained an original cumulus composition (i.e., one that was in equilibrium with the parental magma). The plagioclase is strongly zoned, and the cumulus cores (An59 to An73) are thought to record crystallization from the parental magma.

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