Comparison of lithology and tectonometamorphic evolution of units at the northern margin of the Moldanubian Zone: implications for geodynamic evolution in the northeastern part of the Bohemian Massif
Multidisciplinary research evaluates structural, metamorphic and petrochemical data of selected rock types in different units located in the northeastern part of the Bohemian Massif, Czech Republic: (1) the Strá ek Unit in the northeastern part of the Moldanubian Zone, (2) the Svratka and Kutná Hora units correlated with the Orlice-Sně ník Unit in Western Sudetes as well as (3) the Poli ka, Hlinsko and Záb eh units belonging to the Teplá-Barrandian Zone. Petrochemical data of metasediments of the Poli ka, Hlinsko and Záb eh units are mutually comparable and confirm a lithological affinity to the upper-crustal Teplá-Barrandian Zone. The FeOt/MnO ratios in metasediments of the Strá ek Unit and the Svratka Unit indicate differences in the origin of sedimentary protolith rocks. Relict pre-Variscan structures, including extensive migmatization, and high-grade mineral assemblages with peak metamorphic pressures of 1.4 GPa in skarn bodies, are preserved in the Svratka Unit. The evidence for Palaeo-Variscan (390-355 Ma) HP and UHP events, recorded in the high-grade Kutná Hora and Orlice-Sně ník units, was observed neither in the NE part of the Moldanubian Zone (Strá ek Unit) nor the Teplá-Barrandian Zone (Poli ka and Záb eh units). The Variscan orogenic event imprinted in the Svratka, Poli ka and Záb eh units was the right-lateral slip along WNW-ESE trending shear zones. This deformation was accompanied by metamorphism at T = 580-650 °C and P = 0.5-0.7 GPa (350-345 Ma) and intrusion of numerous small bodies of syn-deformation calc-alkaline granitoids in the Poli ka and Záb eh units. The younger metamorphic fabrics in the northeastern part of the Moldanubian Zone reflect a fast exhumation of deep-seated high-grade complexes at 340 Ma. Metamorphic development in felsic granulites of the Strá ek Unit, metamorphosed c. 340 Ma ago at 850 °C and 1.8 GPa, was followed by decompression to T 790 °C and P = 1.3 GPa and finally T 700 °C and P = 0.4 GPa. In contrast, Běstvina granulite in the Kutná Hora Unit, with the 360 Ma high-grade metamorphism at 800-920 °C and 1.8-2.1 GPa, is free of such a HT-LP overprint. Thus the data indicate that the Svratka and Kutná Hora units, exhibiting numerous mutual differences, should not be considered as belonging to the Moldanubian Zone as they evolved as independent entities. The geochemical data on garnet-clinopyroxene skarns from the Moldanubian Zone, the Svratka and Kutná Hora units do not provide mutually distinguishing features. This is largely due to a very wide compositional variation in rocks in
