High-pressure metabasic rocks from the Kutná Hora Complex: geological position and petrology of exotic lithologies along the segmented Moldanubian margin, Bohemian Massif

Abstract

New occurrences of high-pressure metabasites in the Kutná Hora Unit (KHC) are described. These HP rocks include eclogites (± Ky), Cpx-Grt amphibolites, metagabbros and Cpx-bearing granulites. All the eclogite samples studied are formed of well-preserved HP mineral assemblages with variable degree of subsequent metamorphic overprint. Eclogites from the inner part of the KHC (Roztěž, Bořetice) mostly had a Mg-rich tholeiitic protolith. Chemical, mineralogical and metamorphic data reveal that these eclogites are petrologically similar to the eclogite samples from the better known Běstvina Unit. Eclogites from Bořetice, Poličany and Roztěž preserve relict mineral assemblage from a pre-eclogite stage, enclosed in garnet with prograde zoning pattern. They bear mineralogical evidence of a very high-pressure history, even substantially higher (maximum 8.4 wt. % of Na 2 O in Cpx, P~ 4.3 GPa) than the previously described eclogites from Spačice and Úhrov in the Běstvina Unit. A set of three eclogites from the northern margin of the Moldanubian Zone south of Chotěboř was used for comparison (Bída, Borovský Creek, Krátká Ves). They preserve also a peak pressure record that corresponds to minimum pressures above 2.0 GPa. Better understanding of regional relationships amongst the discussed units can be achieved only using isotopic and geochronological data.

An unusual Ni-Sb-Ag-Au association of ullmannite, allargentum, Au-rich silver and Au-bearing dyscrasite from Oselské pásmo “silver” Lode of Kutná Hora Pb-Zn-Ag ore district (Czech Republic)

“…Serpentinite bodies form an important part of the so-called Kutná Hora Crystalline Complex basement in the Kutná Hora area (Synek and Oliveriová 1993;Štědrá and Nahodilová 2009). Such bodies were encountered by boreholes in southern "silver" lodes both south of town as well as in its historic centre, including the Roveňské pásmo and Oselské pásmo lodes where medieval mining began.…”

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

“…In the Kutná Hora Unit, several stages of regional Variscan tectonometamorphic evolution were identified (e. g. Synek and Oliveriová 1993;Štědrá and Nahodilová 2009;Vrána et al 2009). During an Early Variscan event, the bodies of mantle peridotites and related UHP rocks, with their relict structures, were tectonically incorporated into gneisses and granulites (Synek and Oliveriová 1993).…”

“…It consists of Variscan high-grade rocks, such as migmatites and migmatized paragneisses, with bodies of felsic granulites, ultramafic rocks, amphibolites and skarns (Tajčmanová et al 2006;Schulmann et al 2005Schulmann et al , 2008; (2) the Kutná Hora Unit subdivided into four sub-units of high-pressure migmatites, orthogneisses, paragneisses and mica schists, enclosing lenses of felsic granulites, garnet peridotites and eclogites. The sub-units recorded an early-Variscan HP tectonometamorphic evolution at around 370-360 Ma (Synek and Oliveriová 1993;Kachlík 1999;Vrána et al 2005;Medaris et al 2005Medaris et al , 2006Nahodilová et al 2006;Štědrá and Nahodilová 2009;Vrána et al 2009;Faryad 2009); (3) the Svratka Unit consists of polymetamorphic migmatites, mica schists and paragneisses with amphibolite and skarn intercalations that are cut by bodies of Cambrian metagranites and orthogneisses (Melichar et al 2008;Verner et al 2009). The unit exhibits lithological similarities to the Orlice-Sněžník Unit (basement of Western Sudetes; Buriánek et al 2009b); (4) the structurally overlying Polička, Hlinsko and Zábřeh units are low-to medium-grade volcanosedimentary sequences of Neoproterozoic to Lower Palaeozoic age, classified by some authors as the more strongly metamorphosed eastern part of the Teplá-Barrandian Zone (Mísař et al 1983;Verner et al 2009) or viewed as relics of an allochthonous cover of the Orlice-Sněžník Unit (e. g. Mazur et al 2005;Cháb et al 2010).…”

“…1). More focussed papers stemming from individual parts of this research were published in the special volume "Geological development of the region at the NE periphery of the Moldanubian Zone, eastern part of the Bohemian Massif" of the Journal of Geosciences (e. g. Buriánek et al 2009b;Štědrá and Nahodilová 2009;Verner et al 2009;Vrána et al 2009). We also integrate new geological datasets collected during geological mapping in the region (Project No.…”

Geochronology and petrology of pyroxene-garnet skarns (eastern Bohemian Massif): implications for the source and evolution of the Variscan continental crust

“…Synek and Oliveriová 1993;Kachlík 1999;Faryad 2009;Štědrá and Nahodilová 2009;Verner et al 2009;Perraki and Faryad 2014). Migmatites, granulites and upper-mantle ultramafic rocks containing relics of HP(UHP)/HT mineral assemblages crop out in the uppermost parts of the Kutná Hora Unit, referred to as the Malín and Plaňany sub-units (Vrána et al 2005;Nahodilová et al 2011).…”