Metasomatism and self‐organization of dolerite dyke–marble contacts: Beinn an Dubhaich, Skye

Dolerite dykes which intrude dolomitic marble in the aureole of the Beinn an Dubhaich granite on the Isle of Skye have developed metasomatized margins close to the contact with the (younger) granite in the southern part of Torrin Quarry. These margins display well‐defined mineralogical zones which can be divided into two groups on the basis of composition. Chlorite‐bearing margins display the sequence dolerite | diopside+spinel | chlorite+calcite+magnetite | olivine+calcite+spinel | dolomite, whereas phlogopite‐bearing sequences have a phlogopite+calcite±fluorapatite layer in place of the chlorite‐bearing layer. No spatial pattern is seen in the distribution of the two margin types, but textural and compositional evidence points to an importance of metasomatism by localized infiltration of magmatic fluids in the development of the phlogopite‐bearing sequences. Extensive patterning of the phlogopite‐bearing margins by a process of self‐organization during grain growth has resulted in the formation of alternating silicate‐only/calcite‐only layers parallel to the dyke margin on a millimetre to centimetre scale. Early development of chlorite‐bearing sequences at the dolerite–dolomite contact during contact metamorphism was followed by metasomatism‐controlled growth of phlogopite and patterning at or after the peak of metamorphism associated with the expulsion of aqueous fluids from the crystallizing pluton.