Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Milan Novák, Stanislav Houzar

The HT/LP metamorphism of dolomite marbles in the eastern part of the Moldanubicum; A manifestation of heat flow related to the Třebíč Durbachite Massif

Journal of the Czech Geological Society, volume 41 (1996), issue 3-4, 139 - 146

Three independent metamorphic events are suggested in the dolomite marbles of the Strážek and Moravian Moldanubicum, western Moravia, Czech Republic: HT/HP-MP metamorphism M1, HT/LP metamorphism M2, and retrograde MT-LT/LP metamorphism M3. Since the studied region is tectonically heterogeneous and dolomite marbles are more sensitive than other rocks types to the changes in fluid composition (Ferry 1992), they may be affected in different stages of the metamorphic evolution. Consequently, the M2 metamorphism in dolomite marbles is not directly comparable to the M2 metamorphism in metapelites. The HT/LP metamorphism M2 produced a distinct mineralogical zoning around the Třebíč Durbachite Massif (TDM). Four metamorphic zones, formed by reactions involving the mineral assemblage tremolite + phlogopite + dolomite + calcite + forsterite + chlorite + spinel + clinohumite, were recognized. Two distinct paths of the metamorphism M2 were distinguished in the isobaric T-X_CO2 diagram. The distribution of the metamorphic zones, course of the isograds and textural relations strongly indicate the heat flow related to the TDM. The cause of the heat flow, however, is not sufficiently understood. It seems to be very likely related to the emplacement and consolidation of the TDM amphibole-biotite melagranite, and the heat flow may have acted in early to near subsolidus stages of the intrusion emplacement. The age of the HT/LP metamorphism M2 in the range from 340 to 330 Ma is estimated from the radiometric ages of the durbachite intrusion (Pb-Pb, 343 Ma; Holub et al. 1996) and apparently postmetamorphic lepidolite pegmatites (Rb-Sr, 323-306 Ma; Černý et al. 1995), penetrating the studied metamorphic complex.