Unusual metasomatites (phyolithites) in the Kolvitskiy gabbro-anorthosite rock mass: composition and structural position

Abstract

Complex mineralogical, geochemical, and geological-structural characteristics of a rare collection stone of violet color, phyolithite, in the southwestern part of the Kola Peninsula. This is a metasomatic rock formed under the conditions of brittle deformations on gabbro-anorthosites of the Paleoproterozoic Kolvitskiy rock mass. As a result of potassium metasomatosis, the plagioclase of the initial rocks was replaced by a fine-grained mica aggregate of muscovite-phengite composition with inclusions of Va-aluminoseladonite (up to 20-30 microns). Ba-aluminoseladonite contains 6.6-10.5 % by weight of BaO. Manganese is the only chromophore that accumulates in the rock during metasomatosis. It is manganese that provides the purple-violet color of pseudomorphs of mica according to anorthite. The phyolithites is depleted by REE and has a positive Eu-anomaly. The phyolithites are confined to the areas of fracturing of the north-eastern strike, located in the zone of dynamic influence of the north-western closure of the Onega-Kandalaksha rift of the Riphean age. Other formations (injection conglomerates and lamproites) are also associated with the formation of this structure, which owe their origin to an intense fluid flow.