Acta Musei Moraviae

Metamorphism of dolomitic rocks at the north-eastern margin of the Moldanubicum, western Moravia, Czechoslovakia

Mineral relations in dolomitic rocks of the Strážek Moldanubicum and Svratka crystalline complex confirm their polymetamorphic origin. The oldest metamorphism M 1, characterized by the equilibrium assemblage Phl+Tr+Cal+Dol, is widespread along the whole area studied and it probably corresponds to a medium-pressure regional metamorphism. During the younger metamorphism M 2, three individual phases have been distinguished. The first one is connected with a regional migmatization and metasomatic reaction veins (Mg-skarns) were originated. The most important second periplutonic phase caused a distinct metamorphic zoning. Four zones with the following equilibrium mineral assemblages occur, in order of increasing grade: zone A Phl+Tr+Cal+Dol, zone B Fo+ChlI+Cal+Dol, zone C Fo+ChlI+Spl+Cal±Chu±Dol, zone D Fo+Spl+Cal+Chu+Dol, The mineral assemblage of zone A is a relic of the older metamorphism M 1 and it was often replaced by younger assemblages. The observed sequence of metamorphic zones, presence of clinohumite with X^Chu_F = 0.49 and mineral relations indicate low X_CO2 conditions from 0.1 to 0.4. The third retrograde phase is characterized by a younger chlorite II. Metamorphism M 2 probably corresponds with the Variscan low-pressure regional metamorphism. The youngest retrograde metamorphism M 3 produced antigorite after forsterite.