Abstract
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 Strážek Unit in the northeastern part of the Moldanubian Zone, (2) the Svratka and Kutná Hora units correlated with the Orlice-Sněžník Unit in Western Sudetes as well as (3) the Polička, Hlinsko and Zábřeh units belonging to the Teplá-Barrandian Zone. Petrochemical data for metasediments of the Polička, Hlinsko and Zábřeh units are mutually comparable and confirm a lithological affinity to the upper-crustal Teplá-Barrandian Zone. The FeO t /MnO ratios in metasediments of the Strážek 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-Sněžník units, was observed neither in the NE part of the Moldanubian Zone (Strážek Unit) nor the Teplá-Barrandian Zone (Polička and Zábřeh units). The Variscan orogenic event imprinted in the Svratka, Polička and Zábřeh units was the right-lateral slip along WNW-ESE trending shear zones. This deformation was accompanied by metamorphism at ~580-650 °C and ~0.5-0.7 GPa (352-343 Ma) and intrusion of numerous small bodies of syn-deformation calc-alkaline granitoids in the Polička and Zábřeh 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, which was constrained by post-tectonic emplacement of durbachites at ~339 Ma. Metamorphic development in felsic granulites of the Strážek 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, Běst-vina 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 interpreted as metamorphosed exhalite with detrital material admixture. Skarns from the Svratka Unit preserve clinopyroxenes with elevated jadeite component (0.5-24 mol. %) and prograde compositional zoning in garnet -features obliterated in samples from the Moldanubian Zone and the Kutná Hora Unit.
Introduction
This paper presents a new interpretation of tectonometamorphic processes and their time relationships in the units located along the northeastern margin of the Moldanubian Zone, Czech Republic. Information on this part of the Bohemian Massif plays an important role in elucidation of its geodynamic development in space and time. Attention is focused on lithological, petrochemical, structural and geochronological data related to the preVariscan, as well as Paleo-and Neo-Variscan evolution of the studied units.
We evaluate the results of our multidisciplinary research performed in different units located in the northeastern part of the Bohemian Massif: (1) The Strážek Unit representing the north-eastern Moldanubian Zone, (2) the Svratka, Kutná Hora, Polička, Hlinsko, Zábřeh and Orlice-Sněžník units (Fig. 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. 6328 "Geological mapping of the Žďárské Vrchy Protected Landscape Area"). On the basis of new field structural data we characterize regional fabric patterns and tectonic boundaries of the individual units. For lithological and petrochemical correlations were chosen the most telling rock types, i.e., metapelites, migmatites, orthogneisses, metagranites and skarns. Others, such as granulites and eclogites, were compared according to their P-T history and ages. The P-T estimations from metamorphic assemblages with structural, petrochemical and geochronological data in the selected rocks serve as a basis for unique comparison of lithology and geochemical composition, timing and tectonometamorphic evolution in different units along the north-eastern margin of the Moldanubian Zone. Finally, on the basis of our results and their interpretation, and information published in the literature, we propose a geological model presenting tectonometamorphic processes and their time relationships in the units located along the northeastern margin of the Moldanubian Zone.
Geological setting
The oldest processes recorded in the studied rocks took place in Neoproterozoic to Early Palaeozoic times (~570-530 Ma), i.e. late during the Cadomian Orogeny, at the periphery of the Gondwana and Avalonia . The development culminated by the Cambro-Ordovician magmatic stage (e.g. Linnemann et al. 2008) . The subsequent Late Devonian to Early Carboniferous collision of Gondwana-derived crustal segments with the Old Red continent resulted in assembly of heterogeneous units and created a new geological framework for the western and central parts of the European continent (e. g. Franke 2000 ). This Variscan evolution, i.e. subduction of oceanic crust and crustal thickening associated with high-pressure metamorphism, was dated at ~390-355 Ma (e. g. in the Orlice-Sněžník and Kutná Hora units; Mazur et al. 2005 ; R. Nahodilová, personal comm.) and Neo-Variscan stage at around 340 Ma (Fiala et al. 1995; Finger et al. 2007; Schulmann et al. 2008 Schulmann et al. , 2009 ). These processes were followed by fast exhumation of deep-seated rocks and wrench tectonic activity and references therein). These events were connected with juxtaposition of various crustal segments:
(1) the Moldanubian Zone comprising a heterogeneous complex of high-grade rocks (for a general review see Fiala et al. 1995; Urban and Synek 1995; Vrána et al. 1995; Schulmann et al. 2008 ). The term is used here as defined by Fiala et al. (1995) , except of the Svratka and the Kutná Hora units -below we present evidence indicating that the latter two units evolved as separate entities; (2) the Teplá-Barrandian Zone as the upper-crustal segment including unmetamorphosed to medium-grade Neoproterozoic and Lower Palaeozoic volcanosedimentary sequences (e.g. Chaloupský et al. 1995; Zulauf 1997; Drost et al. 2004) ; (3) the Saxothuringian Zone and Western Sudetes as Neoproterozoic to Lower Palaeozoic rock complexes with tectonically implanted slices of Variscan HP and UHP rocks (Kröner et al. 2001; Mazur et al. 2005) . The units nowadays located at the eastern margin of the Bohemian Massif were thrust over pre-Variscan basement, deformed Late Neoproterozoic granitoids and a tectonically imbricated metasedimentary sequence of Devonian age of the Moravo-Silesian Zone (Schulmann and Gayer 2000) .
The area of our interest is located in the north-eastern part of the Bohemian Massif, and is built by several crustal segments with distinct lithology, composition, tectonometamorphic evolution and age. Proposal of the regional geological division of the Czech Republic published by Chlupáč and Štorch (1992) defined various units discussed in the current paper. These are, from the south to the north ( Fig. 1): (1) the Strážek Unit representing the NE part of the Moldanubian Zone. 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. 2005 Schulmann 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. 2005 Medaris et al. , 2006 Nahodilová 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) . The Polička, Hlinsko and Zábřeh units contain abundant Variscan calc-alkaline granitoids (Buriánek et al. 2003; Vondrovic and Verner 2008) ; (5) the high-grade Orlice-Sněžník Unit resembles in terms of its P-T development and tectonometamorphic evolution the high-grade Moldanubian Zone. However, the ages of HP-HT metamorphism and the following mid-crustal re-equilibration of the Orlice-Sněžník Unit (dated at c. 360-370 Ma and ~345 Ma, respectively) were substantially different (Mazur et al. 2005 ).
Geological features and metamorphic evolution

Strážek unit
The Strážek Unit is composed of Variscan high-grade rocks such as migmatized paragneisses and migmatites with lenses of amphibolites, skarns and tectonic slices of high-pressure felsic granulites (Bory and Drahonín massifs) and upper-mantle ultramafic rocks (Medaris et al. 1995; Tajčmanová et al. 2006; Hanžl et al. 2008a ). The Bory granulite Massif carries numerous boudins of upper mantle peridotite, Grt-pyroxenite and eclogite with P-T conditions of equilibration sarahpineda@example.com GPa and 900-1 000 °C (Medaris et al. 2005 Naemura et al. 2009 ). Felsic granulites of the Strážek Unit preserve early mineral assemblages, indicating HP metamorphic evolution of these rocks under T = 850 °C and P = 1.8 GPa at 340 ± 1.1 Ma (U-Pb on zircon) Tajčmanová et al. 2006) . The subsequent metamorphic events recorded in rocks of the Strážek Unit (partial stages of fast exhumation and re-equilibration) were determined at T ≅ 790 °C and P = 1.3 GPa and, finally, at T ≅ 700 °C and P ~ 0.4 GPa (Owen and Dostal 1996; Tajčmanová et al. 2006) . The overall metamorphic evolution of felsic granulites from Strážek Unit is shown in Fig. 2a (P-T path No. 1).
Kutná Hora unit
The Kutná Hora Unit (see structural sequence, (2) the Kouřim Nappe consisting of orthogneisses and fine-grained leucocratic migmatites, (3) the Mica Schist sub-unit, and (4) the Plaňany sub-unit. The Rataje Mica Schist zone, included by Synek and Oliveriová (1993) in the Kutná Hora Unit, in fact represents a retrogressed marginal part of the Moldanubian Zone (Koutek 1933; Mísař et al. 1983; Kachlík 1999) . Several metamorphic phases, based on mineral assemblages and tied to tectonic events, have been defined in the Kutná Hora Unit. The early mineral assemblage evolved under upper mantle conditions in tectonic slices of Grt peridotites, Grt pyroxenites, eclogites and felsic granulites. The Běstvina sub-unit carries numerous boudins of upper mantle garnet peridotite, Grt pyroxenite and eclogite equilibrated at 3-5 GPa and 850-1 100 °C (Medaris et al. 2006; Faryad 2009 (2009) determined the conditions of the retrogression at 705 ± 97 °C and 1.4 ± 0.2 GPa. This event can be possibly correlated with the high-pressure migmatization in the Malín sub-unit under eclogite-facies conditions, succeeded by regional highpressure mylonitic deformation (Synek and Oliveriová 1993; Vrána et al. 2009 ). The leucogranites intruded in migmatites of the Malín sub-unit were affected by superimposed HP tectonometamorphic event and transformed to Ky-Grt gneisses under a pressure of 0.9 to 1.2 GPa (Synek and Oliveriová 1993; Vrána et al. 2009 ). Key stages of P-T evolution of HP metamorphic rocks from the Kutná Hora Unit are summarized in Fig. 2a. intercalations of dolomitic marbles, amphibolites and skarns (Melichar 1995; Schulmann et al. 2005; Melichar et al. 2008; Hanžl et al. 2008b 
Svratka unit

Polička unit
The Polička Unit represents probably Neoproterozoic to Lower Palaeozoic volcanosedimentary sequence penetrated by calc-alkaline plutonic rocks dated at ~346 ± 6 Ma (U-Pb on zircon; Vondrovic and Verner 2008; Vondrovic et al. unpublished data) . On the basis of the lithological composition, the Polička Unit can be subdivided into three different parts (Melichar 1995) , which are, from south to north: (1) the structurally lowest medium-grained biotite and two-mica paragneisses (± Grt ± Sil) with deformed bodies of metagranites, amphibolites, marbles, calc-silicate rocks and an allochthonous Vír felsic granulite massif; (2) middle part consists of a monotonous complex of medium-grained biotite to two-mica paragneisses (± Grt ± Sil) with abundant calc-silicate nodules and intercalations of metapelites and metaconglomerates; (3) the upper part is composed of mica schist with intercalations of quartzite and paragneiss. Mica schists of the uppermost Polička Unit exhibit the mineral assemblage Qtz + Ms + Bt ± Pl ± St ± Grt ± Pl (± Ky in the eastern part of the unit), indicating peak metamorphic conditions of T ≅ 650 °C and P ≅ 0.8 GPa and a retrograde overprint at 660 °C and 0.7 GPa (Buriánek 2009) ( Fig.  2b , P-T path No. 1). In the metapelites of the middle part of the Polička Unit, the mineral assemblage equilibrated at 570-680 °C and ~0.6 GPa; (Fig. 2b , P-T path No. 2). Relics of sillimanite pseudomorphs after andalusite indicate an older LP metamorphic event (Buriánek et al. 2003) . Estimated peak P-T conditions in allochthonous tectonic slices of Vír granulites dated by Tajčmanová et al. (2010) at ~354 ± 7 Ma (U-Pb on zircon) correspond to T = 860-1000 °C and P = 1.6 GPa (Tajčmanová et al. 2010) (Fig. 2a, P-T path No. 3) . These granulites are accompanied by predominating retrogressed orthogneisses. Mineral assemblages in the surrounding metapelites indicate metamorphic conditions of c. 700 °C and 0.7 GPa, reflecting exhumation of granulites accompanied by partial melting of the metasediments Buriánek et al. 2009a; Tajčmanová et al. 2010) . The U-Pb zircon ages (339 ± 3 Ma and 336.2 ± 1.2 Ma) from granulites of the Vír area and the surrounding amphibolites reflect exhumation of these rocks into a higher crustal level (Tajčmanová et al. 2010) . Monazite (U-Pb) dating at 336 ± 1 Ma on an orthogneiss-like sample by van Breemen et al. (1982) may indicate a post-peak retrogressive event.
Zábřeh unit
The Zábřeh Unit is composed of two lithological subunits, low-grade metapelites and metabasites in the south and paragneisses with intercalations of metavolcanites intruded by numerous sheets of calc-alkaline plutonites in the north (Fajst 1976; Hanžl et al. 2000; Buriánek et al. 2003; Verner et al. 2009 ). The intensity of metamorphism gently increases from the central part to both the south and north. The peak P-T conditions in the northern part were estimated at ~0.6 GPa and ~ 660 °C (D. Buriánek, unpublished data). In addition, effects of local contact metamorphism in narrow zones along the northern intrusive sheets were identified.
Hlinsko unit
The Hlinsko Unit, separated by a NNE-SSW trending polyphase shear zone, extends along the northwestern margins of the Svratka and Polička units. It consists of three metasedimentary groups folded in a great synform elongated NNE-SSW. Some weakly metamorphosed rocks carry fossils of Silurian and Late Ordovician age (Štorch and Kraft 2009). Greywackes and metapelites, in places with layers of metavolcanites, were classified as the Hlinsko and Vítanov groups, metapelites with abundant quartzites were assigned to the Mrákotín Series and graywackes to the Rychmburk Series (Vachtl 1962 ). An anticlockwise P-T path with peak metamorphic conditions of 0.35-0.4 GPa and 600-530 °C was proposed by Pitra and Guiraud (1996) for more strongly metamorphosed parts of this unit.
Orlice-Sněžník unit
The Orlice-Sněžník Unit occurs in the SE part of the Western Sudetes (Lugicum) (Kryza et al. 1996; Mazur et al. 2005; Anczkiewicz et al. 2007; Jastrzębski 2009 ).
It consists of high-to medium-grade polymetamorphic migmatites and orthogneisses of Cambrian protolith age, with outer envelope of staurolite schists and biotite paragneisses. Migmatites and orthogneisses of the Orlice-Sněžník Unit contain abundant eclogite and granulite bodies (Opletal et al. 1980; Mazur et al. 2005 ). The latter rocks experienced an Early Variscan HP (UHP) metamorphic evolution followed by a high-to mediumgrade (HT/M-LP) regional tectonometamorphic overprint (Mazur et al. 2005 ).
Structural patterns
Rocks of the studied units in the northeastern part of the Bohemian Massif recorded complex and polyphase tectonometamorphic processes, particularly during the Variscan orogeny. The orientation and relationships of regional fabrics briefly described below are shown in Fig. 3 .
In the high-grade rocks of the Strážek Unit, the HP(MP)-HT metamorphic stage was followed by rapid exhumation of high-grade rocks. This event was associated with isothermal decompression at high temperatures (Tajčmanová et al. 2010 ). The regional structural pattern in this unit is formed by subvertical, ~NNE-SSW to N-S trending metamorphic foliations, containing rare relics of high-grade fabrics, especially in form of minor rootless to isoclinal folds (Tajčmanová et al. 2010 ). These fabrics were heterogeneously reworked to ~NW-SE to WNW-SSE, flat-lying to gently NNE dipping foliations, in places associated with WNW-ESE plunging mineral lineation. In the Strážek Unit, the formation of this second fabrics is constrained by post-tectonic emplacement of ultrapotassic, Mg-rich granitoids (durbachites) dated by U-Pb method on zircon at 339 ± 2 Ma (A. Gerdes, unpublished data; Verner et al. 2009 ). In general, second flat-lying fabrics are in northern and north-western parts of the Strážek Unit roughly parallel to the boundary with the adjacent Svratka Unit.
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) . Faryad (2009) presented an alternative model of crustal and upper-mantle rocks juxtaposition (Machek et al. 2009 ). Early deformation structures imprinted during the polyphase exhumation of the high-pressure granulites, garnet-kyanite migmatites and other deep-seated rocks of the Kutná Hora Unit are unknown and were at least partly obliterated by younger deformations. To a late generation belong gently to moderately dipping, ~NW to ~NE trending retrograde planar fabrics developed on a regional scale. This event took place in the stability field of biotite and muscovite in the upper Kouřim Nappe, and of garnet + kyanite (± sillimanite) in the Malín and Mica Schist sub-units. This stage was also linked with intense mid-crustal mylonitization and low-angle shearing that resulted in juxtaposition of individual segments of the Kutná Hora Unit and in transformation of alkali-feldspar granite dykes in HP migmatites of the Malín sub-unit into mylonitic garnet-kyanite-bearing orthogneisses (Vrána et al. 2009 ). Numerous lenses of upper mantle rocks also occur in narrow and steep zones of kyanite-garnet mica schists (Štědrá et al. 2008) . Finally, the late tectonic episodes in the Kutná Hora Unit proceeded under the lowtemperature brittle-ductile conditions associated with a syntectonic oriented, and later even random, growth of muscovite (Oliveriová et al. 1995) .
In the overlying Svratka Unit, relics of pre-Variscan tectonometamorphic record linked with ~HP metamorphic conditions (P = ~1.4 GPa) were identified ). In addition, discordant intrusive contacts between Cambrian granites (515 ± 9 Ma, U-Pb zircon age by Schulmann et al. 2005 ) and the surrounding migmatites were described by Verner et al. (2009) . This finding constrains the upper age limit of pre-Variscan high-pressure metamorphism and migmatization of the Svratka Unit to Cambrian times. The Variscan structural pattern of the Svratka Unit is defined by regional metamorphic foliations dipping steeply to moderately to the ~NNW-NE in its western and central, and steeply to the ~SW in its eastern part. These foliations are associated by well-developed stretching lineations (elongated quartz and feldspar aggregates) which plunge under low angles to the ~NW or SE ). Kinematic background of these fabrics suggests a polyphase evolution of right-lateral transtensional to transpressional widely-distributed shear zone. In the southern part of the Svratka Unit these regional fabrics were affected by tectonometamorphic overprint associated with minor partial melting and formation of the gently NNE dipping foliation. During the Variscan Orogeny, the Svratka Unit was affected by regional metamorphism reaching only the amphibolite-facies conditions only ( Fig. 2b ; P-T path 5).
The structural pattern of the overlying Polička Unit is defined by regional metamorphic foliations (pervasive schistosity or compositional banding), which dip steeply to moderately to the NNE-ENE in the central and eastern part, and to the WNW along the western margin of this unit. The foliations bear well-developed, gently plunging NW-SE stretching lineation associated with right-lateral kinematic indicators ). The northern part of The Polička Unit was intruded by numerous bodies of calc-alkaline composition (dated by U-Pb method on zircon at ~352-343 Ma; Vondrovic and Verner 2008; L. Vondrovic unpublished data) . The transition of magmatic to HT sub-solidus fabrics in regional orientation, mostly parallel to the intrusive contacts, indicate syntectonic emplacement of these intrusions in relation to the main tectonometamorphic event ).
In the northern part of the Zábřeh Unit, the regional metamorphic foliations dip moderately to steeply to the ~SSW and are associated with well-developed stretching lineation which plunges gently to the ~ESE or WNW. The intrusive contacts and magmatic to sub-solidus fabrics of abundant calc-alkaline intrusions are roughly parallel to the orientation of the host metamorphic fabrics. The origin of these fabrics in the Zábřeh Unit as well as in the underlying Polička and Svratka units were broadly related with the activity of a regional WNW-ESE directed transpressional to transtensional zone.
Towards the south, the intensity of the transpressional to transtensional fabrics gradually decreases and relics of older low-grade fabrics with a flat-lying orientation could be observed. Finally, the complex of the Zábřeh Unit was affected by sub-vertical shortening. The low-temperature cleavage as well as the axial planes of open folds dipping gently to the SSW were identified. The boundary between the Zábřeh Unit and the adjacent underlying lower to mid-crustal Orlice-Sněžník Unit (Lugicum) is roughly parallel to the regional metamorphic fabrics, however, strongly modified by the Late Variscan right-lateral "Elbe Zone" fault system.
In the upper-crustal Hlinsko Unit several different events in tectonic evolution were identified (Pitra et al. 1994) . The bedding planes broadly associated with orientation of low-grade cleavage were affected by folding during polyphase ~E-W shortening and related development of different sets of crenulation cleavages. The last event of ~E-W shortening of metasediments of the Hlinsko Unit resulted in the formation of a regional WNWvergent synclinal structure. The boundary between the upper-crustal Hlinsko Unit and mid-crustal Polička Unit has a character of moderate-to low-temperature NNE-SSW oriented shear zone. The initial stages of shearing during compression were related to the syntectonic emplacement and subsequent high-temperature deformation of calc-alkaline granitoids of the Miřetín Pluton, recently dated by Vondrovic and Verner (2008, unpublished data) at 345 ± 5 Ma (U-Pb on zircon).
In the southern part of the high-grade Orlice-Sněžník Unit (eastern part of Lugicum), a set of retrograde mid-crustal fabrics was identified (Mazur et al. 2005 ). On a regional scale, along the southern margin of the Orlice-Sněžník Unit, the medium-grade compositional banding dips under moderate angles to the SW and to S. These planar fabrics are associated with well-developed ~NNW-SSE to N-S plunging stretching lineation and indicators of regional extension.
Lithological and petrochemical comparison of selected rocks

Metapelites and metapsammites
The metasediments of the studied units experienced a complicated history of polyphase metamorphism and migmatization (Buriánková et al. 2008; Hanžl et al. 2008b) , which affected the composition of the original sediments with varying intensity. The Polička, Zabřeh and Hlinsko units represent metasedimentary sequences with a predominance of muscovite-biotite to biotite gneisses and lower grade rocks (Buriánek 2010). As these complexes are largely free of migmatization, the main features of sedimentary protoliths are probably widely preserved and thus can be studied by geochemical methods. The primary data used for construction of the whole-rock geochemical diagrams are stored in electronic appendices 1 and 2. In the K 2 O/Na 2 O vs. SiO 2 /Al 2 O 3 (wt. %) plot of Wimmenauer (1984) , gneisses and other metasediments from the Polička, Zábřeh and Hlinsko units form a roughly linear data array mainly in the fields of greywacke and claystone, less frequently mudstone (Fig. 4a) .
Overall, the geochemical features of metasediments of the Hlinsko, Zábřeh and Polička units are all mutually comparable. Major-and trace-element data for metasediments from these units present evidence of their affinity to the Bohemicum (Patočka et al. 2003; Drost et al. 2004; Buriánek 2010) . Manganese-rich metasediments from the Hlinsko Unit (Fig. 4c) can be interpreted as metapelites and metapsammites deposited around submarine springs (Buriánek and Otava 2007). The chemical composition of Polička Unit metasediments probably resulted from mixing between arc and continental-derived detritus. The elevated La/Th ratio, together with decreased Th/Sc and Zr/Sc ratios, in the Hlinsko Unit sediments indicate a larger input from the volcanic arc source (Fig. 4d) . Indeed, tuffitic horizons were indentified in the Vítanov Formation of the Hlinsko Unit.
Biotite to muscovite-biotite migmatites, gneisses or mica schists are predominant in the Strážek and Svratka units. Because of probable modifications due to migmatization (e.g., Inger and Harris 1993; Bea 1996) , some geochemical features of these rocks are discussed separately. Shortage of modern whole-rock analyses from the Kutná Hora Unit prevents correlation for this unit.
In the K 2 O/Na 2 O vs. SiO 2 /Al 2 O 3 (wt. %) plot of Wimmenauer (1984), migmatites and gneisses fall mainly along the greywacke-arkose boundary (Fig. 5a ). Mica schists of Svratka Unit almost form a separate field with lower SiO 2 /Al 2 O 3 and increased K 2 O/Na 2 O values, along the boundary between the fields of arkose and claystone. In the TiO 2 vs FeO t /MnO t diagram (Fig. 5b) , the Strážek This situation suggests supply of geochemically more evolved material in the course of deposition of sediments that became protolith to the metamorphic rocks of the Svratka Unit ( 
neoproterozoic and early Paleozoic orthogneisses and metagranites
Orthogneisses to metagranites are relatively common rock-types in the units along the NE margin of the Moldanubian Zone. Data on the lithological composition and In the Svratka and Orlice-Sněžník units, the studied meta-granitic rocks are very similar in petrology, as well as mineral and whole-rock chemical composition (Buriánek et al. 2009b ). Differences in microstructures and textures relate to distinct geodynamic evolution of the individual bodies. In general, primary magmatic minerals are recrystallized into a mosaic of K-feldspar, albitic plagioclase, quartz, biotite and muscovite aggregates. Apatite, zircon, monazite and ilmenite are common accessories. The whole-rock compositions of samples from the Svratka and Orlice-Sněžník units are similar and contain relatively high SiO 2 (∼76 wt. %), the A/CNK ratio ranges between 1.0 and 1.3, K 2 O + Na 2 O values from 7.2 to 8.8 wt. % and K 2 O/Na 2 O ratios reach 1.4-2.4. These data indicate highly potassic to shoshonitic characteristics of the studied rocks. The rocks are relatively poor in Ba, Nb, Ta, Sr, Hf and Zr, and rich in Cs, Rb, Th, U, K and HREE (Buriánek et al. 2009b) . In general, the genesis of the protolith to the orthogneisses to metagranites from the Svratka and Orlice-Sněžník units can be interpreted as being a result of partial melting of a similar continental crust at the time of the Cambrian extensional event. During the ascent and emplacement, these rocks developed by moderate degrees of melt fractionation (Buriánek et al. 2009b ).
eclogites and metabasites
Most previously published reports on eclogites and other metabasites in the Kutná Hora Unit were focused on a rigid block of the Běstvina granulite (Medaris et al. 2005 (Medaris et al. , 2006 Faryad 2009 ). The eclogite-bearing inner part of Kutná Hora Unit is an area roughly corresponding to the Inner Mica Schist Zone sensu Synek and Oliveriová (1993) and its tectonic contact with the high-grade Malín Unit (Losert 1967) .
Eclogites in the inner part of the Kutná Hora Unit, along with associated garnet peridotites, occur in mylonitized biotite-muscovite gneisses and mica schists, indicating the character of a deep-seated shear zone (Paděra 1972; Medaris et al. 2005) . The zone played an important role in incorporation of the lower-crustal and mantle-derived rocks to upper crustal levels. Several eclogite and Cpx-bearing intermediate rock occurrences have been newly described in the inner part of Kutná Hora Unit near Roztěž, Bořetice and Miškovice . The REE patterns indicate a lower crustal rather than a mantle source for these HP rocks. The P-T calculations yielded minimum pressures above Pertoldová et al. A high-pressure mineral assemblage and peak pressures recorded in one sample of eclogite from the Strážek Unit (Moldanubian Zone) compares to the highest pressures found in the studied area along the Kutná Hora Unit-Moldanubian Zone boundary (P > 2.0 GPa, T = 700-750 °C). On the other hand, the Borek eclogite equilibrated under less extreme metamorphic conditions (Medaris et al. 1998 ).
Skarns
Skarns in the Svratka Unit, in the neighbouring part of the Moldanubian Zone (Strážek Unit) and in the Kutná Hora Unit form competent lenses and layers in gneisses and migmatites and preserve some early deformation structures. The major minerals are garnet and clinopyroxene. The garnet composition corresponds predominantly to the grossular-almandine-andradite series (Grs 75-21 , Alm 78-25 , Adr 65-0 , Sps 23-0 Prp 7-0 ; X Fe = 0.95−1.00), clinopyroxene belongs mostly to the hedenbergite group. The content of the jadeite component is notably increased only in samples from the Svratka Unit (0.5−24 mol. %). Garnets in skarns from the Svratka Unit exhibit well-defined prograde compositional zoning and, together with variation in the jadeite component in pyroxenes and reaction textures, recorded at least three metamorphic episodes, similarly to their host rocks. Garnet compositions indicating peak pressure conditions of metamorphism in skarns in the Strážek Unit are not preserved and the chemical zoning of garnets shows exclusively a retrograde evolution imprint. The oxygen and fluorine fugacities were probably increased in some garnets, but only locally. Although the chemically homogeneous compositions of individual generations of clinopyroxene and epidote do not reflect the prograde and retrograde events in skarns from the Kutná Hora Unit, a prograde compositional zoning in some garnets was observed (Pertoldová et al. (1995) 2009). A summary of the petrological data for skarns is presented in Tab. 2. Altogether 59 whole-rock samples were used for major-and trace-element analyses of skarns in the studied units ). Skarns from the Svratka Unit are highly variable in abundances of major and trace elements (35-55 wt. % SiO 2 , 1-18 % Al 2 O 3 , 1-23 % CaO, 2-47 % Fe 2 O 3 and 2-8 % MgO). Seven samples out of 30 have positive Eu anomaly and low total REE contents. Major elements in skarns from the Moldanubian Zone exhibit a wide variation: 20-60 wt. % SiO 2 , 1-17 % Al 2 O 3 , 5-30 % CaO, 1-66 % Fe 2 O 3 and 0.5 -14 % MgO. The Eu/Eu* ratios cover a wide range of 0.5 to 3.5; the majority of samples are characterised by values near 1.0. The highest Eu/Eu* values are characteristic of samples with low ΣREE.
The geochemical features of the studied skarns do not indicate systematic differences among the three studied geological units, although their tectono-metamorphic development was different. The δ 18 O (SMOW) values for garnet and clinopyroxene from skarn localities in the Moldanubian Zone and the Svratka Unit are low, ranging from -0.1 up to +4.0 (Pertold et al. 1997; Pertoldová et al. 1998 Pertoldová et al. , 2009 Drahota et al. 2005) . Such low values do not support the idea of contact metamorphic genesis ).
Based on the major-and trace-element geochemistry and the geological position, the skarn protoliths are instead interpreted as rocks of mixed detrital-exhalative origin deposited on a sea floor. The total REE contents and type of Eu anomaly are highly variable and indicate variations in the local temperature and redox conditions among the individual layers at a single locality, as well as various localities ). There is also an indication of a rather conservative character of the metamorphism with limited migration of components within the garnet-clinopyroxene rocks. It is probable that hydrothermal solutions, instrumental in the development of skarn protoliths, debouched on the sea floor along fault zones with the character of local extensional rifts. The deposition of exhalites proceeded along such zones, and they were mixed with detrital material in variable proportions. The large variability of the zircon ages in skarn from the Svratka Unit suggests their detrital origin. The fact that most of the data falls between 540 and 580 Ma possibly indicates a source in the rocks of Neoproterozoic age 
* U-Pb age determinations on zircon are interpreted as dating the HP events ** unpublished data R. Nahodilová *** van Breemen et al. (1982) attributed this monazite age to low-T shearing and fluid activity indicate that the previously identified HP-HT event in skarns (Buriánek et al. 2009b; Pertoldová et al. 2009; Verner et al. 2009 ) must have been of pre-Variscan age. On a regional scale, the HP-HT processes including extensive partial melting and emplacement of calc-alkaline granitoids could be related with crustal exhumation in final stages of the Cadomian orogenic processes, or with continental extension during early Cambrian rifting (Linnemann et al. 2000) . In contrast to the published models (e. g. Pitra et al. 1994; Mazur et al. 2005; Schulmann et al. 2005 Schulmann et al. , 2008 , the Svratka Unit was affected by Variscan regional metamorphism reaching amphibolitefacies conditions only ( Fig. 2b ; P-T path 5). This is in sharp contrast to the high-grade Kutná Hora Unit and the Moldanubian Zone.
Tab. 1 Summary of P-T data (°C/GPa
Samples from the Kutná Hora Unit represent mainly Grt-Cpx assemblages with variable contents of the major elements: 22-55 wt. % SiO 2 , 2-14 % Al 2 O 3 , 14-31 % CaO, 2-58 % Fe 2 O 3 and 0.5-4 % MgO. The abundances of trace elements are variable, both for the individual localities and for the individual samples.
Discussion and conclusions
On the basis of the summarized petrological, lithological, geochemical and structural data sets, we present an interpretation of the broadly discussed geodynamic evolution and regional classification of various crustal units bordering the northeastern part of the Moldanubian Zone (Fig. 6) .
lithology and geochemistry

Metasediments
Metasediments from Polička, Zábřeh (eastern part) and Strážek units have FeOt/MnO ratios typical of the continental crust (Maynard 2005) . The contrast in FeOt/MnO values in metasediments from Svratka and Hlinsko units indicate a role of specific redox conditions at the time of deposition and diagenesis of protolith sediments. Details of the scenario are not well understood yet. In any case, the differences in the FeOt/MnO values indicate a major contrast in deposition conditions of the protolith sediments of the Svratka and Strážek units. Both weakly oxidizing or weakly reducing conditions can induce a lower Mn content in seawater (Maynard 2005) .
Sample sets for individual units exhibit characteristic pattern in the high-field-strength elements contents. Low Th/Sc and Zr/Sc ratios and LREE contents are typical signatures of metasediments from the Hlinsko Unit and indicate a considerable proportion of igneous-arc material in the sedimentary protolith. Metasediments of the Polička and Zábřeh units probably represent mixing of arc-and continent-derived material and show affinity to the Hlinsko Unit.
Orthogneisses
As shown by Buriánek et al. (2009b) , protoliths to orthogneisses and metagranites in the Svratka and the Orlice-Sněžník units were likely to have originated by melting of similar crustal rocks and evolved by analogous 
Svratka Unit
Grt-Cpx, Cpx-Grt, garnetite, Cpx skarn, Grt-Hbl, Gru-Cpx processes during Cambrian magmatic event 530-515 Ma ago (U-Pb on zircon) (Kröner et al. 2001; Štípská et al. 2004; Schulmann et al. 2005) . The rock-forming minerals of the studied rocks were affected by Variscan deformation and metamorphic recrystallization under ~MP−MT conditions at ~350−330 Ma (Buriánek et al. 2009b) . Based on published petrochemical data on different types of Cambrian orthogneisses from the Bohemian part of the Moldanubian Zone (e. g. Vrána and Kröner 1995; Breiter et al. 2005 ), these orthogneisses seem essentially different from the studied metaigneous rocks in the Svratka and Orlice-Sněžník units.
Granulites
Granulites are high-pressure rocks equilibrated in fact under eclogite-facies conditions (P = 1.8-2.2 GPa) at high temperatures (T = 800-1 000 °C). Rock-types with granite composition (Ky-Grt-Pl-Kfs (mesoperthite)-Qtz ± Bt) strongly predominate in all the granulite massifs listed above. However, aberrant compositions are also present; e.g. in the Běstvina body these are rocks of paragneiss composition (rich in Grt, Ky and primary Bt, with greywacke-like chemistry), and rare albite-K-feldspar felsic granulites (Vrána et al. 2005 . Granulites form small bodies up to 10 km long, tectonically incorporated in paragneiss-migmatite host-rocks, the latter carrying mineral assemblages indicating significantly lower pressures and temperatures of equilibration. It is of particular interest that granulites in individual units feature contrasting P-T paths during exhumation-related decompression (Tab. 3). Granulites in the Strážek Unit (Drahonín and Bory massifs) exhibit prominent HT-MP/ LP decompression recrystallization (Owen and Dostal 1996; Tajčmanová et al. 2006) , which however lacks in the Kutná Hora Unit 2009). In Běstvina, the composition of the outer zone of garnet in granulites, perfect preservation of kyanite, and the absence of newly formed LP phases all indicate a mild decompression (P ~ 1.4 GPa) in the kyanite field. The major contrast in the P-T path of the two types of granulites (Fig. 2a) excludes any joint evolution as parts of a former coherent unit with the Moldanubian Zone. In addition, the Běstvina granulite in Kutná Hora Unit has age of HP metamorphism by 20 Ma older than Moldanubian granulites (Tab. 3). The third mode of granulite occurrence (Vír) represents a segment directly at the junction of the Svratka and Polička units. These rocks preserve an evidence for decompression recrystallization similar to that in granulites of the Moldanubian Zone (Štoudová et al. 1999; Tajčmanová et al. 2010) , but the original source of these thrust-slices remains uncertain.
High-grade metamorphic events of the variscan age
Granulites as a typical and ubiquitous rock-type are excellent objects for comparison of tectonometamorphic and geochronological evolution in the high-grade Strážek Unit, Kutná Hora Unit and Vír area. Granulites of the Strážek Unit recorded a rapid, nearly isothermal MP-LP decompression recrystallization at ~340 Ma (Tajčmanová et al. 2006; Verner et al. 2009 ). In contrast, granulites of the Kutná Hora Unit are characterized by a perfect preservation of kyanite and an absence of newly formed low-pressure mineral assemblages (Synek and Oliveriová 1993; Vrána et al. 2005 Vrána et al. , 2009 ) (Tab. 3). The Vír granulite body occurs in a tectonic position between the less metamorphosed Svratka and Polička units; however the estimated P-T path is similar to other Moldanubian granulites (Tajčmanová et al. 2010) . In view of the geochronological data of the HP or UHP rocks in the Kutná Hora Unit (the HP crystallization of Běstvina granulite was sarahpineda@example.com ± 5.3 Ma; U-Pb zircon, R. Nahodilová, personal comm.) and in the Orlice-Sněžník Unit (the UHP/HP metamorphic event is constrained to the age range of 360-369 Ma, Klemd and Bröcker 1999; Mazur et al. 2005 and references therein). We suggest that Kutná Hora Unit can be considered as part of the Palaeo-Variscan frame against which rocks of the Moldanubian Zone were exhumed during the Neo-Variscan event (at around 340 Ma; Tajčmanová et al. 2006 ). This interpretation is an alternative to the earlier accepted opinion of Synek and Oliveriová (1993) , who considered the Moldanubian Zone to be a passive paraautochthon unit, upon which the allochthonous partial units of the Kutná Hora Unit were overthrust. Although some geologists refer to the Kutná Hora Unit as belonging to the Gföhl Unit (e.g., Franke 2000; Medaris et al. 2005 Medaris et al. , 2006 Medaris et al. , 2009 Faryad 2009; Faryad et al. 2010) , it is suggested that use of the latter term should be limited to the Moldanubian Zone. Importantly, the mineral assemblages and mineral chemistry in metasedimentary gneisses and migmatites hosting granulite massifs correspond to metamorphic pressures significantly lower than those of the Variscan granulites. This indicates that individual granulite bodies may mark former major discontinuities, along which granulites were emplaced as allochthonous segments from deeper structures. The role of granulites as tectonic markers is somewhat similar to that of metabasic eclogites and peridotites/lherzolites.
Structural evolution
The structural information for the Palaeo-Variscan (390-355 Ma) HP and UHP events identified on the basis of geochronological data in the Kutná Hora and OrliceSněžník Units (R. Nahodilová, unpublished data; Mazur et al. 2005) remains unknown.
In the Moldanubian Zone, only a few geochronological data indicate Palaeo-Variscan processes in garnet-pyroxenites and eclogites (Carswell and Jamtveit 1990; Beard et al. 1992) , no information is available from metasedimentary complexes.
The first well-recorded event of the Variscan geodynamic evolution in the northern part of the studied area (Svratka, Polička and Zábřeh units) were widely distributed WNW-ESE right-lateral, transpressional to transtensional deformations. This event proceeded under T = ~580-650 °C and P = ~0.5-0.7 GPa, in the Polička and Zábřeh units dated by synchronous emplacement of calc-alkaline granitoids at around 352-343 Ma (Vondrovic and Verner 2008, unpublished data; Verner et al. 2009 ). On a regional scale, a similar kinematic framework was documented along the Teplá-Barrandian/Moldanubian boundary, in this case dated by syntectonic emplacement of the slightly older calc-alkaline Sázava and the high-K calc-alkaline Blatná plutonic suites of the Central Bohemian Plutonic Complex (Janoušek et al. 2004 (Janoušek et al. , 2010b Žák et al. 2005 ). In the high-grade Strážek Unit (northeastern part of the Moldanubian Zone), a set of several younger metamorphic fabrics was formed. These reflect partial stages of a very fast exhumation of deep-seated rocks at around 340 Ma: (1) development of relict HP structures in felsic granulites, which correspond to early stages of their lower-crustal evolution dated at 340 ± 1.1 Ma Tajčmanová et al. 2006) ; (2) regional, medium-pressure, steeply dipping NNE-SSW foliations reflecting an episode of exhumation (Schulmann et al. 2008) ; (3) formation of flat-lying fabrics during a sub-vertical shortening of partly exhumed rocks ) and (4) structures of thrusting of Moldanubian rocks over the less metamorphosed or unmetamorphosed rocks of the Moravo-Silesian Zone during lateral indentation of the Brunia continent (Schulmann et al. 2008) . In contrast to results of previously published papers (Tajčmannová et al. 2006; Schulmann et al. 2005 Schulmann et al. , 2008 , the upper limit for all these events in the NE part of the Moldanubian Zone is age-constrained by the post-tectonic mid-to upper-crustal emplacement of the durbachites (Dosbaba and Sulovský 2006; ). Durbachite bodies intruded in the eastern part of the Moldanubian Zone were dated by several authors in the range ~341-323 Ma Verner et al 2009; Janoušek et al. 2010a; Kotková et al. 2010; Kusiak et al. 2010) . However, reliable geochronological data sets from porphyritic Moldanubian durbachites give a clear evidence of emplacement and crystallization of these rocks close to 339 Ma Janoušek et al. 2010a; Kusiak et al. 2010 ). On a regional scale, the flat-lying and thrusting fabrics (points 3 and 4 described above) were in the southern part of the overlying Svratka Unit superimposed on older transpressional to transtensional fabrics defined in the Svratka, Polička and Zábřeh units. The initial phase of the extensional tectonics in this part of the Bohemian Massif began somewhat later than ~338-333 Ma, with formation of the NNE-SSW system of HT to LT mylonitized zones (e. g. Přibyslav mylonite Zone; Verner et al. 2006) . A good example of the presence of this extensional event is partial low-temperature reworking of the NNE-SSW trending shear zone which separates the less metamorphosed Hlinsko Unit from the Polička and Svratka units (Pitra et al. 1994; Vondrovic and Verner unpublished data) . In case of the Orlice-Sněžník Unit (Western Sudetes) a distinct set of various regional fabrics reflecting partial stages of orogenic exhumation by c. ~345 Ma was described (Mazur et al. 2005) . However, these exhumation structures have a different character and orientation compared to the presently studied units. Structural relationships between the southern part of the Orlice-Sněžník Unit and the overlying Zábřeh Unit are unclear. The reason could be the spatial occurrence of conspicuous system of right-lateral WNW-ESE fault structures of the "Elbe Zone", the activity of which is constrained by syntectonic emplacement of the Meissen Massif at 334 Ma and and the intrusion of the Markersbach granite dated at 327 Ma (Hofmann et al. 2008); Linnemann et al. (2008) suggested that the activity started already at around 343 Ma.

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