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Some models consider them to be comagmatic and relate these rocks by processes of liquid immiscibility (Philpotts, 1981) or a specific fractionation trend (Owens , 1989; Duchesne, 1990).
A typical Proterozoic anorthosite–mangerite–charnockite association is exposed in the Lofoten Islands, off the NW coast of Norway, which is dominated by mangerites and charnockites.
2); the nearly inaccessible Moskenesøy anorthosite on the island of Moskenesøy, which is not further described here; and the Eidsfjord anorthosite, which occurs on the island of Langøy.
The contacts between the troctolitic and the gabbroic rocks are gradational.
Detailed estimation of intrinsic parameters () indicates a systematic relationship between the phase assemblages in anorthosites, ferrodiorites, mangerites and charnockites, which is compatible with fractional crystallization of a mafic parental magma.
The commonly observed association of Proterozoic massif-type anorthosites [see Ashwal (1993) and references therein] with jotunitic and mangeritic or charnockitic rocks is still not satisfactorily explained.
In this paper, the first of a series on these rocks, we present the field observations and phase petrology, and determine the conditions under which the intrusions were emplaced.
Subsequent papers will concentrate on the whole-rock and isotope geochemistry of the Lofoten anorthosite suite and will put forth hypotheses for its origin.
The estimation of the intensive parameters for the crystallization of anorthosites, mangerites and charnockites has been hindered by several problems and has therefore rarely been done successfully (Fuhrman , 1988; Kolker & Lindsley, 1989).