Metasomatism and self-organization of dolerite dyke-marble contacts: Beinnan Dubhaich, Skye

Dolerite dykes which intrude dolomitic marble in the aureole of the Beinn a n Dubhaich granite on the Isle of Skye have developed metasomatized margins close to the contact with the (younger) granite in the southern part of To rrin Quarry. These margins display well-defined mineralogical zones which c an 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 t he two margin types, but textural and compositional evidence points to an i mportance of metasomatism by localized infiltration of magmatic fluids in t he development of the phlogopite-bearing sequences. Extensive patterning of the phlogopite-bearing margins by a process of self-organization during gr ain growth has resulted in the formation of alternating silicate-only/calci te-only layers parallel to the dyke margin on a millimetre to centimetre sc ale. Early development of chlorite-bearing sequences at the dolerite-dolomi te contact during contact metamorphism was followed by metasomatism-control led growth of phlogopite and patterning at or after the peak of metamorphis m associated with the expulsion of aqueous fluids from the crystallizing pl uton.