Abstract
Compositional reversals, with rocks becoming more primitive upwards, is a feature at the base of many layered intrusions, such as the Stillwater Complex1, the Muskox intrusion2 and the Great Dyke3. Mechanisms such as contamination by an evolved melt from partial anatexis of country rocks or reaction between cumulus minerals and intercumulus melt are usually inadequate to explain these features4. A major reversal at the floor of the Hyllingen Series, part of the Fongen–Hyllingen complex, Norway, is consistent with crystallization during gradual elevation of compositionally stratified magma up an inclined surface in response to the influx of dense, primitive magma. During enlargement of the chamber, increasingly primitive magma comes into contact with the sloping floor just below the roof and an inverted sequence of crystalline products derived from the stratified magma develops. An intrusive mechanism of this type seems likely for layered intrusions which possess basal Mg-enrichment trends.
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Wilson, J., Engell-Sørensen, O. Basal reversals in layered intrusions are evidence for emplacement of compositionally stratified magma. Nature 323, 616–618 (1986). https://doi.org/10.1038/323616a0
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DOI: https://doi.org/10.1038/323616a0
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