It is proposed to undertake a detailed petrogenetic study of an exceptionally well exposed section through a major layered pluton of massif-type anorthosite: the Paul Island intrusion, Nain, Labrador. Most mapping and sampling and much preliminary petrography and geochemistry have been completed. The Intrusion displays a stratigraphic section about km thick that contains most of the textural and compositional varieties of massif-type anorthosite and a comfortable lens (1.5 km thick) of the most primitive mafic cumulates in the Nain complex. Characteristics of the earliest unit suggest crystallization of about 50% plagioclase at great depth prior to diapiric emplacement. Later, fluid replenishments established a chamber that permitted bottom accumulation of anorthosite. Zoning of phenocrysts in the uppermost unit implies that plagioclase remained suspended within an actively convecting, periodically replenished chamber. Many fine-grained anorthosite and mafic dikes have compositions and occurrences that are appropriate for parental liquids to different cumulate units. The major goals of this study are: (1) to establish the character and origin of parental magmas to the anorthosites, (2) to establish the state of the magma and the mode of emplacement, and (3) to understand processes that operated in anorthositic magma chambers.
