Many cumulates in layered intrusions contain plagioclase crystals that are compositionally zoned in terms of their major elements, and, less commonly, in their 87Sr/86Sr isotopic ratios. Major-element zoning in plagioclase is best explained by trapped liquid in the pore spaces between cumulus crystals, which is a result of the complex interplay between the rate of crystal growth and the cooling rate. Isotopic zoning in feldspars likely reflects crystal growth in a magma that is becoming, or has become, isotopically contaminated through wall rock partial melting and assimilation processes. Mineral-scale isotopic zoning, such as detected in plagioclase, can be used to infer the cooling rates of layered intrusions.

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