Mechanism of Mineral Reactions Inferred from Textures of Impure Dolomitic Marbles from East Greenland

Mineral assemblages and chemical compositions of minerals foundin impure dolomitic marbles embedded in gneisses and migmatitesof the E. Greenland Caledonian fold belt (Scoresby Sund) suggestthat the marbles were metamorphosed near 630 °C at 5 kbpressure. The analysis of complex textural and mineralogicalrelations among minerals such as dolomite, calcite, forsterite,pargasite, chlorite, spinel, diopside and phlogopite led tothe conclusion that the major mineralogical features of therocks were probably caused by sodium metasomatism at constanttemperature and pressure. The effect of the inferred sodiummetasomatism may be summarized by three schematic reactionsall involving modal changes of excess dolomite, calcite, forsterite,chlorite and spinel: (a) nucleation and growth of pargasite,(b) resorption of phlogopite, and (c) growth of pargasite fromphlogopite.