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- Anorthosites and their environment
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Anorthosites and their environment
Abstract
This joint paper, written in honour of Professor Paul Michot, explores differences in interpretation of some well-studied anorthositic terrains which are geologically similar in many respects.
The Adirondack anorthosites and the Nain complex in Labrador are considered anorogenic plutons with long fractionation histories, giving rise to a great variety of associated rock types. It is concluded that anorthosite massifs are essentially anorogenic, and related in space and time to each other and to the rapakivi plutons of Fennoscandia (D. de W.).
The Rogaland complex of southern Norway, at the other hand, is considered a synorogenic pluton, which differentiated from a parental magma to some degree hybridized by crustal material. Here the conclusion is that anorthosites are emplaced at different times in the tectomagmatic cycle, and at various levels in the earth's crust (J. C. D. and J. M.).
A joint conclusion is that the parental magma must have had a monzogabbroic to granodioritic or monzonoritic to quartz-monzonoritic composition.