The still widely cited view of the Palisades sill, northeastern United States, being differentiated largely by vertically directed, olivine-dominated fractionation is not supported by available structural, petrographic, and geochemical data. Rather, the sill can be viewed as a sheetlike composite intrusion, possibly made up of multiple magma types common to the Mesozoic eastern North America magmatic province. The famous olivine zone of the Palisades sill may have resulted from a separate late intrusion of olivine-normative magma and not from gravity-controlled, olivine-accumulation processes. Pyroxene-dominated fractionation accounts for much of the vertical and lateral compositional variations in the Palisades sill and other related intrusions from the province.

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